Extended Experimental Investigations (EEIs)

Here are 300 suggestions to get you started on your Physics EEI. I've added some thoughts on possible variables for the first 200.

· The Thermocouple
One device used widely used in science, industry and medicine to measure temperature is called a thermocouple. It consists of two wires of two different materials that are joined at each end. When these two junctions are kept at different temperatures a small voltage occurs. This voltage drop depends on the temperature difference between the two junctions. The phenomenon is called Seebeck Effect. The measurement of the voltage drop (or emf) can then be correlated to this temperature difference. Thermocouples are among the easiest temperature sensors to use and are very popular because they're generally very accurate and can operate over a huge range of really hot and cold temperatures. Since they generate electric currents, they're also useful for making automated measurements. Be warned about information you get off the internet about thermocouples. One popular site says a thermocouple is "...a junction of dissimilar metals that creates a voltage you can relate to temperature." This misinformation continues to appear on company web sites, in application notes, and in articles. You could make a simple thermocouple from copper and iron wire (see diagram below) using boiling water and icy water to calibrate your device. Then you could investigate the cooling curve (and time constant) when the hot end is allowed to cool in a gentle breeze. Or you could look at ways of forming the junction (twisting, soldering, welding). Or how about different alloys and what factors influence the voltage (resistivity perhaps). There are lots of things that would make a great EEI.

· The World’s Simplest Motor
The "Homopolar Motor" has to be the world’s simplest. It was invented in 1821 by Michael Faraday. You’ll find ones on You Tube purporting to be simple but not as cool as the one below. “How does it work?” was set for the 2009 IYPT competition in China. Briefly, (and I don’t want to give you too much help) when you touch the wire to the side of the magnet, you complete an electric circuit. Current flows out of the battery, down the screw, s******* through the magnet to the wire, and through the wire to the other end of the battery. The magnetic field from the magnet is oriented through its **** faces, so it is ******** to the magnet's axis of symmetry. Electric current flows through the magnet (on average) in the direction from the center of the magnet to the ****, so it flows in the ****** direction, perpendicular to the magnet's axis of symmetry and <snip> so the magnet begins to spin. Neat! For an EEI you could investigate angular speed vs voltage etc. Think stroboscope when you think speed. There’s a good article in The Physics Teacher, February 2005. Somewhat surprisingly, this is more than just a curiosity: motors of this design are currently being developed for quiet, high-power applications.

· Roof colours - white vs black
Nobel laureate Steven Chu, former professor of physics at the University of California and now U.S. Energy Secretary in President Obama's administration says "white paint is what's needed to fix global warming". However, Steven Chu said, even if we paint every roof white, "there was no silver bullet for tackling climate change, and said a range of measures should be introduced, including painting flat roofs white. Making roads and roofs a paler color could have the equivalent effect of taking every car in the world off the road for 11 years." That sounds like an ideal EEI. One Australian company sells just the thing: White Roof Shield is a white coating which reflects 80% of the sun’s radiation. They say it "helps reduce interior cooling loads of air conditioned structures, resulting in savings of both energy and money. Even buildings without air conditioning stay cooler because roof surface temperatures are significantly reduced". Put some roofs of different amounts of whiteness in the sun for some time and measure the temperature of something underneath (maybe air, water). Maybe a heating curve is best. May need more than three trials, and what's the best way to produce this (mixing black and white paint proportionally, black masking tape etc). What about flat paint vs satin vs glossy?

· Tennis Racquet - Sweet and other spots
On the face of the tennis racquet, there are several points that are important to players; these are the centre of percussion, the vibration node, the best serving spot, the best returning spot and the dead spot. A couple of the spots are shown on the diagram below. The centre of percussion is one of the two "sweet spots" of the racquet. This is because at the point of impact between the centre of percussion and the ball, the hand can feel no impact. This is due to the fact that the centre of percussion is located near the centre of the face of the racquet. You can easily find out what all this means and about the other sweet spot. A good EEI would be to test the 'coefficient of restitution' (ratio of bounce height to drop height) of different parts of the face. Perhaps clamp the racquet in a vice and drop a tennis ball on different position of the face and noting bounce height as a fraction of drop height. Does drop height affect the coefficient of restitution? Is the type of ball important? Does a temperature change shift the sweet spots? Are new racquets better than old? Is aluminium better than graphite? Does string tension play any part? The possibilities are endless. The photos of professional players show that the serving spot is high and the return spot is low.

· Danger inside a hot car
After rescuing 20% more children from locked cars last summer than the previous year the Royal Automobile Club of Queensland has urged parents not to leave children locked in cars. The RACQ says that on a typical Australian summer day, the temperature inside a parked car can be 30° - 40°C hotter than outside the car. That means that on a 30°C day, the temperature inside the car could be as high as 70°C and 75% of the temperature increase occurs within five minutes of closing the car. They also say that darker-coloured cars can reach a slightly higher temperatures than lighter-coloured cars (I would have though much higher temperatures); and that large cars can heat up just as fast as small cars. The key variables are obvious for an EEI and having a data logger would be great. But some others worth considering are the colour of interior trim; having the windows down a bit, or even fully open; dark vs light colours; big vs small; time of day (angle of sun); and window tinting. It looks easy but controlling the variables will be important.

· Air Cannon
Projectiles such as tennis balls, oranges and potatoes can be launched from a plastic pipe using compressed air. The device is called an air cannon and relies on a cylinder of air compressed with a bicycle pump being quickly released into a smaller plastic barrel via a quick-acting valve (hand operated or solenoid). There are many designs on the internet but for the purposes of a good EEI a small cannon should be made and the pressure restricted to a maximum gauge pressure of about 30 psi (200 kPa) for safety. You could examine the effect of pressure, barrel length and diameter on distance. Mr Forzatti and his physics students at Siena Catholic College on the Sunshine Coast, Queensland made a straight one, not like the folded design shown below. Most of the designs on the internet look dangerous and may be prohibited under Queensland weapons legislation so negotiate the design and safety considerations with your teacher. If in doubt - don't do it.

· Parachute descent and mass.
Parachutes are not only used for sport but for dropping soldiers into war zones and delivering food and medicine to flood and drought ravaged countries. Even though they've been around for several hundred years it wasn't until after WW2 that the apex vent was invented. You could do an EEI to find out how drop time is affected by mass, canopy area, size of apex vent, number or length of strings, canopy shape and so on. That's Genevieve Ash on the right having a bit too much fun.

· Hertzian Waves
Many early experiments with radio used sparks as detectors and as sources of electromagnetic radiation. A good EEI would be to investigate the electromagnetic nature of radio waves. You could find out if the strength of the signal decreases of intensity with distance from the transmitter, and to investigate electromagnetic shielding. One way would be to tune a transistor radio (not digital) between stations. The radio almost certainly has an automatic gain control and so will be more sensitive when tuned between stations. However the background noise - also broadband noise - will be stronger too. Hold one end of the wire to one end of a 1.5V battery. With the other end of the wire briefly scrape the surface of the other battery terminal, making sparks that will be visible in dim light. You could use a CRO to measure the loudness of the crackle on the radio. What happens with distance, voltage of the transmitter, shielding (paper, metal, glass) between transmitter and receiver.

· Hot Air Balloons
Physics teacher at Urangan State High School, Hervey Bay, Queensland - Alan Whyborn - has his students investigate hot air balloons and the conditions needed for the balloons to catch fire. He said that he once saw a colleague in Canberra make hot air balloons from shopping bags, using metho and cotton wool, simply wired across the handles of the bag. They took them outside (on a still day), lit the metho and off they flew. On a number of the bags the opening collapsed in a little and the bags caught alight. He was horrified at the sight of flaming balloons releasing drips of burning plastic as they drifted casually through the air! He says: "In August 2007 in Canada, a fire broke out in a hot air balloon. Two people were killed. Could it be that the air in such a balloon may become excessively hot and cause the material of the balloon (the “envelope”) to ignite and burn?" This sounds like the basis for an EEI: factors influencing the ascent of a hot air balloon. Alan gives the following important tips: large, really thin/light garbage bags must be used, and get the lightest cane available (craft shop). Also, if the balloons are allowed to fly to the ceiling, they can tilt and the bag might catch fire, so the anchor is very important (plus it holds the balloon in place while the pebbles are added to the gondola to increase the payload). Also, still air is necessary - inside the lab with fans off is great. If done carefully with appropriate preparation and warnings, there is very little hazard. In some cases, students have had a "fuel load" big enough to create sufficient heat to shrink the bag. Ordinary cotton wool balls are perfect, but not compressed or the rate of heat release might not be sufficient to get necessary lift. Click here for: Procedures and safety notes from Urangan SHS.


Constructing: a light cane loop and sticky tape holds the bag end open. Fine wire across the middle is used to attach the fuel ball and gondola.	Fuelling: a cotton ball soaked in metho is attached by a hook to the centre wire.	Inflating: the ball is lit and the bag fills. A slack safety cord tethers the bag to the floor.	Loading: pebbles are added to the gondola to achieve neutral buoyancy.

· Insulation and cooling of hot water
Bubble wrap is a good insulator but how would the rate of cooling of a bottle of hot water vary with the number of layers of wrap? Newton's law of cooling makes reference to the rate of cooling and the difference in temperature between the object and room temperature (but he also said 'in a gentle breeze' that most Physics books forget to mention. Perhaps the initial temperature is important, or perhaps the volume.

· Photonics and fibre optics
The Australian Government's proposed National Broadband Network is planned to connect 90% of all Australian homes, schools and workplaces with broadband services using fibre optic cable. Understanding the physics behind fibre optic technology is set to become even more important to those involved. As signals pass along the fibre they get weaker (attenuate) as the light gets absorbed and scattered on its way through. Attenuation is one of the most important measurements for optical transmission systems because it determines the maximum distance between repeaters. With new glass that has been developed for optical fibres, light can travel more than 10 km before 90 per cent of it is absorbed. This is a big improvement over ordinary glass which loses 90% in 20 metres. Some interesting experiments involve modelling optic fibre with glass rod (eg stirring rod) and making different bends in a number of pieces. Compare energy losses ("curvature loss" or "macrobend loss") as a function of angle. Try dipping the rod in different liquids (to simulate the cladding) and measure the attenuation again. Try different thicknesses of rod. Put scratches on the glass. I'm tld that if the radius of the bend is greater than 20 times the diameter of the fibre, then losses are neglibible. Hmmm!

· The Stud Finder
The stud finder is a device is designed to indicate the presence of wood studs behind wallboard by detecting changes in capacitance. Generally, each detector contains a capacitor whose conductive plates are arranged so that both plates lie in the same vertical plane (see figure below). When the device is placed in contact with a wall, that plane is parallel to the wall, causing electric fields generated by the pair of plates to penetrate behind the wallboard. As the detector is moved across the wall, those fields are affected by what dielectric material is present, resulting ultimately in changes in capacitance. Those variations are detected and then indicated by changes in light and/ or sound intensities. For the stud sensor, the presence of a wood stud behind the wallboard causes the capacitance to increase in that region due to an increase in dielectric constant. For an EEI you could investigate the properties of a commercial studfinder (about $25): do different wood types have different capacitance; effect of moisture content of the stud; metal vs wood; electrical cables (on and off); effect of thickness and so on. Perhaps you could make a model one and compare.

· Datalogging Power Generation
The fundamental principles of electricity generation were discovered during the early 1830s by the British scientist Michael Faraday. His basic method is still used today: electricity is generated by the movement of a loop of wire near a magnet (or vice versa). You could do an EEI on the factors influencing the generation of an electric current. A good way would be to use a Pasco (or similar) datalogger and record the voltage induced in a coil (air solenoid) by a spinning magnet nearby (see photo). The experiment could be repeated with the spinning magnet closer to the coil, or the number of turns on the coil can be increased or decreased. These variations will cause the area for a half-cycle to change, but again this can be shown to be independent of speed. If the number of turns on the coil is changed by a known ratio, the area for a half-cycle should change by the same ratio. You could also set up three coils at 120° to each other. Photos courtesy of Mark Dixon, Clifton College, Bristol, UK.

· The Physics of the Bungee Jump
National Geographic magazine first reported this sort of jump by Pentacost Island natives in 1955. It was later popularised by A. J. Hackett in NZ. The conversion from GPE to EPE is an interesting one but the relationship is far from simple. You could model a bungee using rubber bands and brass weights, or do something more dramatic. You may even find out why they say bungee jumping is glue sniffing for Yuppies. One of the problems is that as the jumper falls the mass of rope hanging below is getting less so acceleration is actually greater than g. That sounds wrong but it appears to be true. Have a look at: Understanding the Physics of Bungee Jumping from Physics Education V45(1) 63-72 (January 2010) and you'll see what I mean.

· What type of waterwheel is the most efficient?
A water wheel is a machine for converting the energy of flowing or falling water into more useful forms of power, a process otherwise known as hydropower. In the Middle Ages, waterwheels were used as tools to power factories throughout different counties. The alternatives were the windmill and human and animal power. Overshot (and particularly backshot) wheels are said to be the most efficient types; with claims that a breastshot steel wheel can be up to 60% efficient (but who'd believe Wikipedia?). Why not make this the subject of an EEI and see if efficiency depends on fall height, rate of flow, paddle area and so on? Great fun if you're good at constructing things. But be warned - it's no good just making a couple and testing them; you need to vary some of the parameters and hypothesise how this may affect effiiciency.

· Flight of a Golf Ball
This was first investigated by Prof. Peter Tait of Edinburgh University in 1900. His son was Scottish National Golf Champion who could hit a ball further than the mechanics formulas of the time predicted because they didn't know about spin. It still makes a great EEI as there are so many things to investigate. Try: angle vs. number of dimples; try sanding off one-quarter of them and putting gloss paint to make it smooth again; then try half (see below), and three-quarters. Design a device for giving it a constant velocity, eg falling pendulum, or something spring-loaded. Vary angle, try at different speeds. How to get top spin?

· Gravity car
An old favourite for physics and engineering competitions is the 'gravity car'. It involves the transfer of gravitational potential energy from a falling weight to an attached small model car which acquires kinetic energy. There are many designs but a simple one is shown below. The brass weights are attached to a string passing over a pulley attached to the car. The string is wound around the axle. As the weights fall and lose GPE, the string turns the wheels and the car begins to move. Your EEI could investigate the optimum falling mass and cart mass combination for maximum acceleration or velocity. Remember - as you increase the falling mass (and thus DGPE) you are increasing the mass of the whole system. This will have implications for acceleration. A great EEI and lots of scope for demonstrating advanced thinking.

· Descent of a ball bearing in oil
It is vitally important that motor oil doesn't get too thin in summer nor too thick (too viscous) in winter otherwise the car engine might seize. A Falling Ball Viscometer uses the rate of descent of a ball bearing to measure the viscosity of a liquid. Try investigating drop time vs. temperature, type of oil (20W50 etc), size, mass or density of ball, width of column. This can be very messy; oil is such a pain to clean up you're probably used to having someone else clean up for you. So don't be surprised if your teacher seems reluctant. Perhaps try a golf ball in a measuring cylinder or water at different temperatures.

· Singing wine glass
You can make a wine glass sing a pure tone by rubbing your degreased and wetted finger around the rim. Vibrations are set up in the wall of the glass and resonance occurs in the air column. When you increase the volume of water inside the glass the frequency of the sound changes (increases/decreases? - you find out). A lot of it is counter-intuitive! But is the pitch proportional to the circumference, the diameter of the glass or the amount of liquid in the glass? Physics books give wayward opinions and you could finally work out who is right and what factors are involved. Capture the sound on a CRO and work out the frequency. Four variations you could try are shown below. The last one has a solid column in the glass so there is less water but the same water level. Or you could compare liquids of different density or viscosity; or non-polar (hexane) with polar (ethanol). Don't try to do too many variables or you'll run out of time.

· Air resistance and the descent of a balloon
Inflated party balloons fall slowly to the ground because of their large cross-section for their weight (low density). Students often think a good EEI would be to investigate the effect of air resistance on falling objects (eg tennis, ping pong and cricket balls) but mostly the objects fall too fast and the measurement error is too great. A great EEI would be to suspend a motion sensor (ie a sonic ranger) from the ceiling and let an inflated balloon fall from underneath it. You could increase the mass (add paperclips etc) and redo the measurements keeping diameter constant. Then you could keep the mass constant and change the .... (you work it out!). It might be good to try dropping a heavy ball (even a volleyball) as a comparison.

·     Stability of a bicycle
Have you noticed how you can ride a bike with your hands off the handlebars and you don't fall over? But if you give it a push just how long does it take to fall over? Variables - linear speed, mass, angular speed of wheel, rotational inertia of wheel I = mr²; add lumps of clay or lead to rim).

·     Sliding friction - variation with speed?
You've no doubt measured the coefficient of friction by pulling a wooden block across various surfaces at constant speed and measuring the force with a spring balance. Probably you've found that friction is independent of surface area and normal reaction force (laws of da Vinci, Amonton and Coulomb). That's fine but you might recall how difficult it is to get constant speed. The problem is that friction does change with speed (particularly for dry, unlubricated metals) although it may be not noticeable. A good EEI would be to extend this idea and measure the displacement or speed as a function of time as you add different weights and try different surfaces. Think about grouping the surfaces into elastically hard and elastically soft (rubber, textiles). Some computer interface packages have a "smart" pulley that gathers data. The diagrams below may give you some ideas.

·     Pulling a nail out
Use a claw hammer to pull a nail out of wood. See suggestion below. Need to compute mechanical advantage of lever. How does force (calculate F₁r₁ = F₂r₂) vary with depth of nail, diameter of nail, grain orientation (end, side, top), density of wood. How does a pre-drilled hole (varying diameter) help or hinder? Scientific American had an article in about 2007. They said the force to pull a 50mm nail out of end-grain of seasoned hardwood was about 260N, but the force became lower as it came out. How would you measure the force as a function of distance embedded. Now that's difficult!!

·     Cooling rates of ice in a freezer
Some people say that warm water freezes before cool water but that seems to violate common sense and physics principles. You could investigate some factors: Rate vs. container size, thickness or type of material, covered/uncovered, initial temperature, stirred/unstirred. Good one for thermometer probes and a computer interface, eg TI-CBL2, Casio, Datamate etc.

·     Loop the Loop - measuring "Jerk"
For an object travelling in a circle, its centripetal acceleration is given by a_c= v²/r. If it is moving in a vertical circle, its speed may change from bottom to the top, so does its acceleration. The rate of change of acceleration is known as "jerk" - units: ms^-3. Examine the jerk of an object to model the motion of an aircraft in a loop-the-loop. By the way - railway engineers try to keep jerk below 2 ms^-3 to avoid passenger discomfort.

·     Hot spots in a microwave oven
Your aim could be one of either (or both): to measure experimentally the wavelength of microwaves in a microwave oven; and/or where are the hot spots and how do they correspond to antinodes based on the answer to the first question. Try investigating temperature rise vs. location; differences between horizontal and vertical planes; which materials should I use - butter, chocolate, water, grapes.

·     Beam Deflections
Structures such as buildings and bridges consist of a number of components such as beams, columns and foundations all of which act together to ensure that the loadings that the structure carries is safely transmitted to the supporting ground below. Normally, the horizontal beams can be made from steel, timber or reinforced concrete and have a cross sectional shape that can be rectangular, T or I shape. The design of such beams can be complex but is essentially intended to ensure that the beam can safely carry the load it is intended to support. Planning to do engineering at uni next year? Then why not get a head start and do a "beam deflection" EEI? Here's the scenario: as a structural engineer you are part of a team working on the design of a prestigious new hotel complex in a developing city in the Middle East. It has been decided that the building will be constructed using structural steelwork and, as the design engineer, you will carry out the complex calculations that will ensure that the architect’s vision for this new development can be translated into a functional, economic and buildable structure. As part of these calculations you must assess the maximum deflections that will occur in the beams of the structure and ensure that they are not excessive. It is said that the deflection of a spring beam depends on its length, its cross-sectional shape, the material, where the deflecting force is applied, how the beam is supported and so on. But perhaps this is only true when you use homogenous, linearly elastic materials, and where the rotations of a beam are small. I'm not going to give you too many ideas! Have a look at Scott Boon's EEI photos below (Bundaberg North State High School, Queensland). He's an engineer in the making.


The load was water in a bucket.	Laser pointer helped with accuracy.

·     Descent of golf balls down an incline
If you roll a golf ball down an incline you should note that as the angle increases so too does the velocity. You could measure time vs. angle; time vs. distance. Is acceleration uniform? Why do similar looking balls give different results; perhaps it is to do with their construction (see 2-piece, 3-piece and 4-piece types below. Maybe it is to do with their dimples or hardness (Novice = long, soft; Intermediate = very long & soft; Power = straight & very soft; Titleist = extremely long, and so on). Try removal of dimples! Use a light gate at bottom to measure final velocity; how does this compare with 2 x v_av?


·     Stopping distance of toy cars along the floor
For sliding friction on an incline, the coefficient of friction μ = tan θ for constant speed; but for rolling friction it may not be. You could let a car roll down a ramp on to the horizontal floor and see how long a distance it takes to stop. How does this vary with the angle or height; coefficient of friction of floor material; effect of weight of car and so on. What are the practical implication for this? Does twice the mass (eg a truck) mean twice the stopping distance?

·     Hot ball bearing behaviour
If you place a hot steel ball bearing on parallel metal track near a supermagnet, the ball sits there for a while and then zooms off. I have seen the video clip made by Mr Mark Young and his physics class at Churchie (some frames below) but just what is going on here? Something to do with cooling below the Curie Temperature. It would be an interesting experiment to try. I have a hypothesis but have never had time to test it.

· Carbon dioxide sound lens
Sound, like light, can be focussed using a concave reflector. Sound can also be focussed using a refractor - just as a convex glass lens is used for light. A biconvex gas lens will bend sound waves so that can be focussed providing the gas in the lens has a density higher than the surroundings. You could make a sound lens by filling a balloon with CO₂ (from dry ice or a cylinder). You could also make a lens by cutting two circles out of plastic sheeting and taping or gluing the perimeter. Your EEI could be to investigate how the amount of refraction varies with the different densities of the gases inside and outside the balloon, the degree of curvature, the relationship between focal length and wavelength of sound, effect of temperature, ... the factors are endless. If SO₂ wasn't so dangerous you could try that too.

· Submarine Buoyancy - "Up, up and away"
Submarines have been a source of wonder, awe, fear and excitement since Bushnell built his Turtle in 1776. Super heroes and secret agents, in both fact and fiction, have been in and out of them quite literally for centuries. Scientists have gone to great lengths to show that the carefully faked submarine adventure of Jack Sparrow in Pirates of the Caribbean was physically impossible. Here's a neat EEI from Sandgate State High School courtesy of physics teacher Ewan Toombes. It goes thus: Stage1 - Design and build a Robot Submarine using plastic bottle ranging from a 1.25L softdrink bottle up to a 4L juice container which can be trimmed to neutral buoyancy so that it “floats” just above the bottom of the pool at a depth of 1 metre. Stage 2 , The Escape – Release or inject a known volume of gas into the ballast tank(s) by remote control (something that operates above but works under water that allows you to inject a known volume of gas into your submarine) that will allow it to escape to the surface carrying a "treasure" of known mass that was resting on the bottom and attached to the submarine by a slack piece of string. Stage 3 - Measure the acceleration of the submarine as it rises. Stage 4 - Calculate the acceleration it should have had due to the excess gas and use your research to explain any difference between the two. That's the start. Now think of some variables to manipulate, propose an hypothesis, justify it, design an experiment and go and investigate. Photo taken at Sandgate SHS.

·     Slip or Tip - the limiting point for falling over
If you stand a wooden block on it's end and give it a slow push with a pointy object (eg a pencil) it will either slide along or tip over. See figures below. The question to investigate is: what factors influence the slip or tip height? Is it friction, area of base, mass of block....?

·     Coupled pendula
If you have a rigid horizontal support such as a rod between two retort stands and hang two pendulums (pendula) of different lengths off the rod you get a strange effect when you start one oscillating. The "rigid" rod is not quite as rigid as you may think. It's not quite as simple as some books make out and in fact makes a great EEI (particularly if you like a bit of maths).

·     Battery discharge as a function of temperature
You'd think that a frozen AA cell (battery) wouldn't work as well as one at room temperature. But how true is this? The voltage appearing at the terminals at any particular time, as with any cell, depends on the load current and the internal impedance of the cell and this varies with, temperature, the state of charge and with the age of the cell. How should you discharge the cell? What size resistor will do the trick in a manageable time? Manipulated variables: temperature, load resistance. Dependent variables: voltage or current?

·     Energy output of a solar panel
Measure current as a function of the angle of incidence of sunlight (all within a short period of time eg 30 minutes); measure current when collector is perpendicular to rays during the day (how should that go?).

·     Magnetic Braking I - sliding down an incline
Magnetic braking relies on eddy currents. An eddy current is an electrical phenomenon discovered by French physicist Léon Foucault in 1851. It is caused when a conductor is exposed to a changing magnetic field due to relative motion of the field source (eg a magnet) and conductor. For example, when a permanent magnet moves over a sheet of metal (such as aluminium), eddy currents are set up in the metal and these can act as a brake on the motion (Lenz's Law). If you let a magnet slide down an incline on a sheet of alfoil then perhaps the braking current may be observed when compared to a control. A sheet of OHT plastic on top of the alfoil will keep it from tearing. But what if you use two sheets of alfoil separated by plastic? Or what if the alfoil is doubled in width; or twice as thick, or if the metal had higher resistance (eg Si rich iron), or the speed was slower, or faster, or the foil was slotted? Oh, the possibilities!

· Magnetic braking II - model car
The experiment described above can be varied to consider magnetic braking of a toy car. The materials I used were a simple toy car, a magnet, a slab of dielectric material (wood or plastic) and another one of a non-magnetic metal (aluminium or copper). The magnet used was of neodymium iron boron (NdFeB), which had been removed from a broken computer hard disk drive. The high level of magnetic field created by these magnets makes it possible to create interesting demonstrations of electromagnetism and electromagnetic induction and a beaut little EEI. Fix the magnet to the underside of the car with a rubber band and let it run down a wooden incline, and then compare it to motion down an aluminium incline. It will be slower because of the magnetic braking. But how much slower. As it speeds up is the breaking force still the same. Will it be less if the magnet is further away? If so, does it obey some inverse square law. Oh what fun.

· Magnetic braking III - rolling magnet
A neat experiment in magnetic braking is to roll a supermagnet down a aluminium channel and compare its motion when a non-metallic (plastic or wooden) channel is used. I've tried it and it works like a charm. However, I wonder if the braking force is related to the speed of the magnet (if so, why?) and this could be investigated by varying the angle. There is a little bit of friction with the walls of the channel but this would be similar for the non-metal and possibly could be calculated as it would be common to both. Would cutting slots in the channel make any difference? If you think so you'd need to work out why and justify your conjecture first. The bait cast fishing reel in the photo below is one that uses magnetic braking to prevent backlash when casting. It provides some sort of counter torque.

· Magnetic braking IV - pendulum
A final suggestion is to investigate a supermagnet pendulum. If a pendulum is allowed to oscillate between two pieces of aluminium (or other metal) the eddy currents should slow it down. You could compare a freely swinging magnet with the same one swinging as in the photo - between two aluminium slabs (I used two hotplates on their sides but I could detect some attraction to some hidden iron). One difficulty is coping with terrestrial magnetism which loves to interfere. Some variables: length of string (related to period and hence speed), distance between plates. I had a good time with this until the bell went for the end of lunch.

· Crash Cushions
Crash Cushion (or Crash Attenuators) are rubber devices that protects the motorist from a blunt object such as concrete wall or guard rail. Inside of the cushions is a very high density foam. As the vehicle hits the front of the system, the system collapses and these devices cushion the impact; like an accordion. You could model a barrier and decide on optimum type of material and size. Variables: perhaps force vs. compression, deceleration vs. thickness, mass of vehicle vs compression. Look at KE, momentum, impulse, spring constant.

· Medical physics - blood oxygen and altitude using a pulse oximeter
Here's a difficult EEI that may be of interest if you are thinking medical physics. It looks at the changes in blood oxygen with altitude using a device called a "pulse oximeter" - a clip-on sensor used in hospitals to monitor oxygen saturation in the blood. You'd have to have access to one of these. The body is remarkably effective at maintaining blood oxygenation at a constant level, typically between 95 and 100% (meaning that arterial blood is carrying between 95 and 100% of the maximum amount of oxygen that it can possibly carry). However, if you climb a mountain, it is found that blood oxygenation levels reduced by 6% per 1000 m of ascent. Pulse oximetry is based on the different absorption spectra of oxygen-rich oxyhaemoglobin and oxygen-poor deoxyhaemoglobin at red and near infrared wavelengths. It exploits this difference by shining two wavelengths of light, one red and one near infrared, through tissue and measuring the resulting light intensity. Two light sources, usually LEDs at wavelengths of around 650 and 900 nm, are held at one side of a convenient site (typically the finger or earlobe in adults, or the foot in babies) and a photodetector held opposite records light transmitted though the body. So, if you are planning a skiing or hiking trip with a group of people you could measure O₂ levels at different altitudes, across a wide range of people (different ages, skin colour, weights) and see what you get. Developing and testing an hypothesis is the main challenge. Look at the criteria for your EEI and see how you may meet them. See Physics Education 2009, V44 (6), p 577.

· Surface Tension of liquids
You've seen examples of surface tension in action: water striders walking on water, soap bubbles, or perhaps water creeping up inside a thin tube. Surface tension is defined as the amount of energy required to increase the surface area of a liquid by a unit amount. So the units can be expressed in joules per square meter (Jm^-2). You can also think of it as a force per unit length, pulling on an object. It can be used to explain why sap rises in trees, how the surfactant works in our lungs and why waterproofing agents work. You could construct a simple balance to make some measurements (see below). Your EEI could look at how surface tension changes with concentration of solute (eg soap) or with temperature. If you choose to compare the surface tension of different liquids then you'd have to have a reason (in terms of physics principles) for doing so.

· Coupled pendula - metronomes on a skateboard
I've never tried this but I've been told it works. If you set two metronomes to the same frequency and place them on a skateboard (or a base that is free to move), they will not be synchronised and will get out of step. However, if you wait long enough they will synchronise and become 'phase locked' or 'mode locked' as they are forced to endure the driving force of each other. Biology abounds with examples of synchronization: cells in the heart beat together, audiences often applaud together, fireflies in South-East Asia flash in synchrony, cicada emerge together, etc. The earliest known scientific discussion of synchronization dates back to 1657 when Christian Huygens built the first working pendulum clock. Huygens studied systems of two pendulum clocks mounted on a common base. He observed that the clocks would swing at the same frequency and 180 degrees out of phase. This motion was robust, after a disturbance the synchronized motion came back in about half an hour. Huygens spent some time exploring this curious phenomena. You could investigate what starting conditions are necessary for phase locking. Maybe start with presstisimo (208 Hz) which is the fastest setting and make them 180° out of phase. No more hints but you should see the amazing demo on You Tube: http://www.youtube.com/watch?v=W1TMZASCR-I

· Doppler Effect of source moving in a circle
The rise and fall in pitch of a sound source as it move towards and away from you can be simulated using a small 9 volt buzzer (from Dick Smith) and battery attached to a rotating platform. I've seen a 100cm aluminium bar attached at it's centre to a small electric motor. If the buzzer is at one end, the battery in the middle and a counterweight at the other end, you'll have endless fun. Fix a microphone to the benchtop 50 cm from the motor. Record the sound at rest and then at different speeds. Analyse using spectrogram software easily obtainable on the web (eg Audacity).

· Doppler Effect of source moving on a pendulum bob
Similar to the one above but with the buzzer attached to a pendulum bob. You can calculate the speed mathematically at any point on it's journey and relate this to the waveform. No more hints!

· The Large Amplitude Pendulum
Speaking about pendula, the formula for a small amplitude pendulum T = 2π√(l/g) has to be modified when a larger angle (eg up to 90°) is used. The modified formula can be found in newer university physics texts and on the internet. However, you could investigate the effect for yourself and see if the modified formula really is an improvement. Just remember that the approximation sinθ = θ when the angle is in radians. One hypothesis could start "if the release angle is increased then the accuracy in measuring 'g' will ............ when the mass of bob and the length of the.............are kept...............".

· Simple Pendulum - feeling the Tension
To measure the period (of one oscillation) of a pendulum accurately, you usually measure the time for 10 oscillations and divide by 10. When your manipulated variables are length (L) or mass (m) you make angular displacement (θ) a controlled variable. However, this is a bit of a lie as the angular displacement decreases with every oscillation - it is not constant. I know it is not much but could be a significant source of error. It comes about from the friction of the bob in air, and, of the friction between chains of molecules in the flexing (bending) of the string or nylon fishing line at the top. The intramolecular forces between nylon polymer chains in nylon 6, 6 are the quite strong hydrogen bonds so the loss of energy could be significant. But as you know from your study of SHM, the forces on the bob are not constant - they are the least when the bob reaches it's maximum displacement (see figure below). So if you could measure the tension (T) in the string with a force sensor and capture the data with a laboratory interface, a plot of force vs. time should give you the peaks that you need. I won't say any more; this could be a great EEI.

· Optimising a solar water heater
Build a model from designs you can find on the internet; determine what you are going to measure (rate of temp increase perhaps), then optimise or at least determine the effect of changing various variables (area, number of tubes, paint colour (gloss vs. matt), glass thickness (one sheet, two sheets etc). You should be able to hypothesise what the changes will do to the measured variable. Are there any mathematical relationships? Are any unexpected?

· Concrete hydration
The importance of concrete in modern society cannot be overestimated. Look around you and you will find concrete structures everywhere such as buildings, roads, bridges, and dams. There is no escaping the impact concrete makes on your everyday life. Concrete is prepared by mixing cement, water, and aggregate together to make a workable paste. It is molded or placed as desired, consolidated, and then left to harden. Concrete does not need to dry out in order to harden as commonly thought. The concrete (or specifically, the cement in it) needs moisture to hydrate and cure (harden). When concrete dries, it actually stops getting stronger. Concrete with too little water may be dry but is not fully reacted. The properties of such a concrete would be less than that of a wet concrete. The reaction of water with the cement in concrete is extremely important to its properties and reactions may continue for many years. You could make up thin slabs of concrete in a shallow trough with different amounts of water and test their breaking strain. What if you were unable to get fresh water - would seawater be just as good? The possibilities are endless.

· Hysteresis and rubber bands
When you stretch a rubber band and then let it go, you can notice that the band does not behave like a spring. A rubber band, made of latex and rubber, does not return to its exact original shape after being stretched. This is an example of a phenomenon called hysteresis. Small vehicle suspensions using rubber (or other elastomers) can achieve the dual function of springing and damping because rubber, unlike metal springs, has pronounced hysteresis and does not return all the absorbed compression energy on the rebound. Mountain bikes have frequently made use of elastomer suspension, as did the original Mini car. By studying the relationship between the rubber band during stretching and unstretching as weights are added or removed, you can determine the amount of work done on the rubber band, the amount of energy (in joules) lost by the band and plot a hysteresis curve. Of course, you'd need more than one rubber band.

·     Buckling Height
Galileo pointed out in 1637 that an animal's bones must be proportionately stronger, therefore thicker, in a large land animal if they are not to be crushed by the animal's own weight; hence the mass of the skeleton must rise relatively greater than body mass. This is also of concern in the growth of trees and in the design of vertical beams for buildings (eg cylindrical piles). You could investigate how the strength of a hollow cylinder varies with diameter when keeping the mass and length the same. Maybe use cylinders of rolled-up A4 paper and look at crush loads for different diameters and configurations (cylinder, oval, sqaure, rectangle).

·     Pressure/Depth Sensor
The deeper you go into a liquid, the greater the pressure on you from the surrounding liquid. This is the principle behind the depth charge - an anti-submarine weapon intended to defeat its target by the shock of exploding near it. Most use explosives and a fuze set to go off at a pre-determined depth. Would it be possible to design and build a device (not a bomb, just a sensor) that responds to increasing pressure with depth and a LED turns on at set depths? You’d have to figure out a pressure sensor and then try out a model in a swimming pool. It sounds very hard but could be a great EEI.

·     The Gaussian Gun
If you arrange several steel ball bearings and a strong (Neodymium) magnet as shown in the picture, you are on the way to constructing what is called a Gaussian Gun. When a single ball bearing (far left) is given a gentle push it is accelerated towards the magnet and strikes it at high speed. The ball to the far right shoots off at a higher speed. Why? That's for you to work out and what factors are involved. If the final ball the strikes another set of magnets and balls mayhem ensues. There are many factors to examine here: but the number of balls on the right, and the distance between these and the next are vital. How to measure things - that's the question; maybe some photogates. You could even make a muitimagnet gun for extra velocity. Have a look on You Tube to see some in action.


·     Fresnel lenses and magnification
Magnification of an overhead transparency on an overhead projector (see below); dissect an old one with the power cord removed to examine the optics; or open up a new one; what thickness lens would be needed to replace the Fresnel lens (pronounced Fr-nell); is magnification related mathematically to the distance between object, Fresnel lens, top lens and screen?

·     Strength of spaghetti strands
Spaghetti makes an interesting substance for modelling structures. Three civil engineering students (pictured below) designed and built a bridge weighing 193 grams that was capable of supporting 53 kilograms. The use of spaghetti is a great way to demonstrate some basic principles of engineering because it reacts to the five internal stresses and strains within a structure – tension, compression, bending, shear and torsion. For an EEI individual strands can be investigated for their strength by hanging weights on middle of horizontal strand. You could measure displacement ('sag') vs weight for various span widths; or different diameters of the strand. I'm told the sag varies with the weight according to a 4th-power rule; and the diameter vs sag is an inverse cube relationship. But that's only hearsay.

·     Arrow range and draw
A bow is a device that converts slow and steady human force over a distance (Work) into stored Elastic Potential Energy (in the form of tension in the Bowstave, Limbs, or Prod). This energy is converted into Kinetic Energy upon release of the Bowstring, and a great deal of that kinetic energy is transfered to the arrow. A bow is basically a spring which stores energy to be put into the arrow. However, 'draw' is not necessarily proportional to the force applied; and therein lies the complication. You could examine range vs. draw vs. launch angle; variation in range with type of tail fletch; comparison of velocity by ballistic pendulum and range.

·     Gyroscope spinning in the one plane
A spinning object on a moveable axis will keep spinning in the same direction even if the supports move. The first practical use was for an artificial horizon in British ships in 1744. The gyro-compass was invented in 1908. But under what conditions will the axis remain in a fixed position? What of bearing friction, rotational speed?

· Arrow accuracy and tail fletches
Tail fletches are the feathers on the ends of arrows. You could do an accuracy comparison of Bulldog, Native and Pope & Young fletches; or you could try setting the fletches straight with no offset, straight with an offset, or left and right helical fletching. The combinations are enormous. You could investigate
the errors with different fletches; why? What's the hypothesis? What is important - range or accuracy & why?

· Guitar Strings and Mersenne's Law
You should be well aware that as you tighten a guitar string it's pitch (sound frequency) increases; and the thick strings wound with copper produce a lower frequency than the lighweight steel or nylon ones. This is the basis of Mersenne's Law: the fundamental frequency of a vibrating string is proportional to the square root of the tension and inversely proportional both to the length and the square root of the mass per unit length. You could investigate this for yourself but the Law is only the starting point; it's no good just proving the law by using a recipe-style experiment - that's hardly the recipe for a good EEI. You'll have to extend the experiment: does the law have limitations, does it work at all temperatures; how much stretching do the strings undergo; do they obey Hooke's Law?

·     Guitar Pickup
The electric guitar pickup works on electromagnetic induction principles. A magnet inside a coil induces magnetism in a steel string nearby and when the string moves...voila! A humbucker is a modified pickup that has two coils in opposition to reduce the effect of stray AC signals. You could model a pickup and test the effect of spacing, magnet strength, coil windings, size of string etc; and then test the ability of a humbucker to reject external noise. I told my students that Jimi Hendrix used to rewind his pickup coils to make them more sensitive. The students said "who's he?".

·     Factors affecting the frequency of an organ pipe
This is another music-related investigation you could undertake - but it also applies to the exhausts of motor cars and bikes; for example, auto engineers make the exhaust pipes such that they resonate at certain desirable frequencies. For some V8s with a separate tailpipe from each bank of cylinders they run a 60mm pipe down each side and put a 50mm pipe joining them to generate beautiful beats. So organ pipe physics is used all over the place!   Why not investigate end correction for different wavelengths and diameters of a simple pipe (eg PVC plumbing pipe); and for open and closed pipes. How does temperature play a part?

·     Spacing between successive turns of a slinky suspended vertically under its own weight
Measure spacing vs. distance along spring; effect of added weight; why would anyone want to know this - what's the point? Compare a steel and plastic slinky. How do their spring constants vary?

·     The 555 Time Machine
The 555 microchip is an integrated circuit invented by Hans R. Camenzind in 1970 and introduced to the world in 1971. Using simply a capacitor and a resistor, the timing interval can be adjusted and so can be used for numerous applications including timers, clocks, switches, security alarms and tone generators. Circuits are freely available on the internet. An idea for an EEI would be to test the accuracy of the timing circuit. The problem is - how do you measure it's accuracy when the stopwatch you would used is based on a 555 timer anyway? Perhaps you could see if the error is related to the tolerances of the resistor and capacitor; or perhaps you could make a few of them and see how they vary; or perhaps you could see how reliable they are with varying temperatures.

·     Pullling a spool of cotton by a thread
An old favourite: investigate the conditions for rolling forward or backward; angle; effect of weight and surface friction - see diagram below. Again, why would you want to know this?

·     The Kelvin water dropper
The Kelvin water dropper, named for Lord Kelvin (William Thomson), is a type of electrostatic generator. Kelvin referred to the device as his water-dropping condenser. The device uses falling water drops to generate voltage differences (up to 6000 V) by utilizing the electrostatic induction occurring between interconnected, oppositely charged systems. It is possible to build a very simple high-voltage generator which has no moving parts. By dripping water through some old soup cans, several thousand volts magically appear. An EEI would be to investigate the conditions under which the potential differences appear: size of cans, distance drops fall, rate of flow and so on.

·     Turbine efficiency
This EEI models a device known as a "fluid coupling" similar in many ways to the processes occuring in the automatic gearbox of a car. A fluid coupling is a hydrodynamic device used to transmit rotating mechanical power from one part to another. It also has widespread application in marine and industrial machine drives, where variable speed operation and/or controlled start-up without shock loading of the power transmission system is essential. In essence it consists of two turbines (fan like components): one connected to the input shaft; known as the pump, impellor or input turbine. The other connected to the output shaft, known as the output turbine or just plain turbine. A good investigation would be to see what factors affect the efficiency of the conversion of mechanical energy from one fan to the other. You could do this with air as the fluid, or try it in water or oil (your teacher may hate you using oil in the lab at it makes one enormous mess and is hard to clean up). For a more viscous water-based liquid you could start with honey and gradually dilute it. The photo below uses a low-voltage motor turning a fan to provide the wind, which blows against another fan to drive a low-inertia dynamo (the turbine). It is up to you to develop an hypothesis and a way of measuring input and output energies (perhaps using a voltmeter). An efficiency vs speed graph would be fascinating.

· Windpower: the world of carbon reduction.
Wind energy is plentiful, renewable, widely distributed, clean, and reduces greenhouse gas emissions when it displaces fossil-fuel-derived electricity. It is considered to be more environmentally friendly than many other energy sources and worthy of our investigations. Most wind turbines seem to be 3-bladed whereas domestic fans seem to be 3, 4, or 5 bladed. As well, wind turbines can have adjustable blade angles. You could make some model turbines hooked up to a small electric motor and measure the voltage produced when you blow air on it. How does blade angle, blade length, number of blades etc affect performance?

· Yagi Transmitter
A Yagi-Uda antenna is familiar as the commonest kind of terrestrial TV antenna to be found on the rooftops of houses. It is usually used at frequencies between about 30MHz and 3GHz, or a wavelength range of 10 metres to 10 cm. You may know that they are directional and when being installed they have to be rotated until the strongest signal is found. A Yagi transmitter has a characteristic pattern of signal strength as shown in the figure below. An EEI that a Year 12 radio enthusiast from Sandgate State High School (Brisbane) undertook was to study the radiation pattern of a halfwave 5-element Yagi antenna transmitting a signal from a 147 MHz VHF transmitter. Suggested dependent variables are distance and angle. If this means nothing to you then this EEI would not be any fun. If you are in to radio communications or know a ham-radio enthusiast then it could be good. The student was Gal Strasberg (seen below) and his physics teacher was Ewan Toombes. You don't need to make the antenna - just buy one. And you'd have to buy, borrow or hire the VHF transmitter and the field strength meter. Gal bought the transmitter online from a radio communications supplier (Andrews Communications), and the built the field strength meter himself using a basic tuned circuit similar to the one at: http://www.zen22142.zen.co.uk/Circuits/rf/fsm.htm

· String unwinding on a pole
Measure time for n turns; variables: initial length, radius of pole, angle, weight of bob.

· Kicking a football
Measure time of contact using Alfoil strips on the ball and shoe as a timing switch; measure time of flight, range, angle, pressure).

· Electric strain gauge
A strain gauge is a device used to measure the strain of an object. Invented in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, such as superglue. As the object is deformed, the foil is deformed, causing its electrical resistance to change. You could compare one to a length of nichrome wire and measure it's resistance as weights are added; try parallel; try other wire. Do they behave in a similar fashion? If not, why not?

· Roller Coaster Loop-the-Loop
Have you noticed that the loops in a roller coaster rise are not circular; they are ellipses. The reason is to do with the maximum centripetal acceleration the body can take before blacking-out. Now, they don't want you to black out as it would hold up the ride, and you wouldn't be able to go an buy their overpriced food. Model one using flexible track and try varying ratios (major axis : minor axis). Vary the speeds; contemplate conservation of mechanical energy. What are the various combinations of speed and axis ratios needed to keep acceleration below the safety limit?

· Air damping
A 'damper' is a device that eliminates or progressively diminishes vibrations or oscillations. A shock absorber in a car deadens (dampens) the up-and-down movement because it contains a dampner called a dashpot which resists motion via viscous friction. The resulting force is proportional to the velocity, but acts in the opposite direction, slowing the motion and absorbing energy. Vertically suspend a brass 'weights' hanger from a spring and measure oscillation period as masses added; then make a cardboard damper and try again. Is decay of period logarithmic? Vary area of damper.

· Modelling sporting equipment as solid pendulums
The "sweet spot" for a piece of sporting equipment is the region of the bat or racquet which gives players the optimal result from a stroke. It is sometimes said to be the centre of mass, centre of percussion, the power centre, the area that gives the most bounce, the are which gives the least vibration to the holder's hands etc etc. There are twenty different definitions on the web. A good one to investigate is the centre of percussion (where a perpendicular impact will produce translational and rotational forces which perfectly cancel each other out). Another is to model the bat to a solid pendulum. You could make a comparison of a cricket bat, baseball bat etc with metre ruler etc.

· Factors affecting the restitution of bouncing ball
The coefficient of restitution or COR of an object is a fractional value representing the ratio of velocities before and after an impact. But as it is difficult in the lab to measure velocities you can measure bounce heights and work out the velocities. Actually restitution in just the ratio of the square of the heights. You could investigate if restitution decreases as the number of bounces continues (or just change the starting height). As a matter of interest, he International Table Tennis Federation specifies that the ball must have a coefficient of restitution of 0.94. What is the effect of temperature, gas pressure, mass etc? If you are comparing balls (eg golf vs tennis vs cricket you would need to know why you are ding this and what you hope to show. The fact that they are different may be of little interest in terms of physics concepts.

· Friction and temperature
Have you seen racing car drivers spin their wheels before a race to get the tyres hot and sticky and to increase friction (perhaps)? Just how does temperature affect friction? Are intermolecular attractions reduced as temperature increases? A neat little EEI would be to measure frictional force between two surfaces and then heat them up (in an oven) and measure it again. Have a look at the nosewheel of this Italian Air Force G222 transport plane at 2002 Riat airshow!

· Newton's Law of Cooling
In 1700 Newton published his Law of Cooling (in Latin) which stated that the rate of change of the temperature of an object is proportional to the difference between its own temperature and the ambient temperature (i.e. the temperature of its surroundings) when "placed in a wind blowing uniformly, and not in a quiet Air, that the Air heated by the Iron might always be carried away by the Wind, and the cool Air might succeed in its place". Most texts leave out the last sentence. I checked 17 university Physics texts at Griffith University and only one mentioned that the Law only applies in a breeze. Throughout the 1800s physicists also forgot about the breeze until a physicist at Edinburgh University (Prof. Crichton Mitchell) reviewed the original in 1887 and pointed it out to everyone. A good EEI would be to see if Newton's Law of Cooling applies with or without a breeze, and if the strength of the breeze makes a difference. An old shotput with a drilled hole for a thermometer probe might be a good start.

·     Atwood machine and 'g'.
The Atwood machine was invented in 1784 by Rev. George Atwood as a laboratory experiment to verify the mechanical laws of uniformly accelerated motion. Atwood's machine is often used to measure 'g'. But how accurate is it? Surely the friction in the pulleys would defeat accurate measurement. But perhaps friction is lower when the masses are lower and maybe accuracy improves. Perhaps it is more accurate when the difference in masses is great. Who knows. Why don't you find out?

·     What is the 'best' way to heat water; kettle or microwave oven?
You'd think that a kettle would be as it is designed to heat water; but the microwave is more modern and could be better or more efficient. But what is efficiency? What does 'best' mean here? How is efficiency affected by volume of water; time of heating. Should energy input be kept constant, or just time?

·     A rubber band under stretch and relax
Elasticity is an important factor in the design of building frames. For example, what is known as the "hybrid frame" design provides elasticity in response to dynamic loading caused by an earthquake, and the effects are like a flat rubber band held at both ends and stretched. The rubber band will stretch but not break, and then return to its former state. A hybrid frame building reacts much the same way, resisting the lateral forces of the temblor and reverting to a static state after the action stops. You could model the behaviour of this building material using a rubber band and look at a number of factors: how many times can it be stretched; effects of temp; coefficient of restitution vs cross-sectional area of rubber, and so on.

·     Optimise a water rocket
A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel - the engine of the rocket - is usually a used plastic soft drink bottle. The water is forced out by a pressurized gas, typically compressed air. As the water is ejected the rocket's mass becomes less so less force is needed to maintain acceleration; but as the gas expands it's pressure becomes less and can provide less force. How do these competing factors affect the motion of the rocket. You could look at height or time of flight vs initial mass of water, pressure, nozzle area, mass of rocket. Explain the physics to justify your hypothesis or will you do it by trial-and-error?

·     Meteorites and tsunamis
When an asteroid hits the ocean at a typical speed of 70000 kmh^-1 there is a gigantic explosion. The asteroid and water vaporize and leave a huge crater - typically 20 times the diameter of the asteroid (that is, a 100 m asteroid will create a 2 km diameter crater). The water rushes back in, overshoots to create a mountain of water at the middle and this spreads out as a massive wave - a tsunami. The centre of the crater oscillates up and down several times and a series of waves radiate out. You could investigate how the diameter of the crater relates to the diameter, speed, density, mass of the meteorite. I think a video camera might be necessary for this. If this is too awkward perhaps letting objects of different size, mass, speed etc fall into sand (fine, coarse) might be easier.

·     The angle of a meteor strike and crater shape
Why are impact craters always round? Most incoming objects must strike at some angle from vertical, so why don't the majority of impact sites have elongated, teardrop shapes? If you throw a stone into sand on the beach at even a small angle from the vertical you get an elongated crater; so why not for real meteors? The answer seems to be that the physical shape and direction of approach of the meteorite is insignificant compared with the tremendous kinetic energy that it carries. Elliptical craters may only show up at really small angles for meteors. However, a good EEI would be to model impact angle using marbles in sand, or in flour. A layer of cocoa powder on top of the flour makes it easy to photograph.

·     Thermal conductivity
Thermal conductivity, k, is the property of a material that indicates its ability to conduct heat. It is very important in industry. One interesting way I’ve seen is to drop a cube of metal into water in a polystyrene cup and measure the rate of heating of the water. Seems so simple but is it accurate? Is surface area important? Doesn’t the rate of warming slow down as the difference in temperature gets less? An interesting application of thermal conductivity testing is shown below. Here they are trying to get an accurate value of the existing soil conditions for a geothermal project.

·     Investigate conservation of momentum and kinetic energy in two dimensions
A good EEI if you like billiard table physics. Measure the effect of 'English', spin, position struck etc; any access to TI /Casio/Pasco photogates? This is too much fun to be Physics.

·     Analysis of projectile motion using a digital video camera.
Get hold of a high definition video, and high speed with frame rates 300fps, 600fps and 1200fps (although 1200fps is small image and needs really good lighting). The Casio EXILIM Pro EX-F1 Digital Camera (<$1,000) is supposed to be great according to teachers who have used it for motion capture. One teacher said that as the Casio Exilim EX-F1 is not available in Australia he imported it from Hong Kong via eBay. All up cost with a 16G memory card and extra battery was just under AU$1000. His other comments can be viewed by clicking Casio EXILIM. However, the problem with high definition videos is that they are compressed to the hard drive and this causes some issues with some data capture programs such as Logger Pro.
(Some ideas: football, springboard diver motion: s/v vs t; what variables to change; must collect first hand data).

·     Interference effects of sound in a room
Audio engineers go to a lot of trouble working out the best placement of loudspeakers in a room. For example the recommended placement for 7.1 Channel Surround Sound is:   Front speakers should be placed at the edges of the screen, toed in to face the central listening location, and the tweeters should be ear height. The center speaker should be placed behind the screen (when using projection) or over or under a TV, and as close to ear height as possible. Side channel speakers should be placed on side walls, to the left and right of the listening position, equidistant from the front speakers and the rear speakers. Rear channel speakers should be placed on side walls, slightly behind the listening position, and should have a normal high-quality monopolar construction. Front speakers should be at ear height and surrounds should be above ear height. See diagram below. It is even hard enough just getting the placement right for a simple two-channel stereo. A part of the problem is because even a pair of sound sources (speakers) emitting a monophonic sound generate interference in the room - even without considering reflections off the back and side walls. An interesting EEI would be to try one and then two speakers in a room (say left and right front) emitting a pure tone from a frequency generator and measure and account for the nodes and antinodes (as measured with a microphone and CRO). You can decide the controls and manipulated variables (but keep it simple).

· Specific heat of metals
It is pretty useless just measuring the specific heat using a calorimeter and water; that's hardly an EEI deserving of an "A" standard. But if you can optimise the method and improve it's accuracy then you could be on to a winner. How do volume of water, initial water temp, mass of metal, size of calorimeter (copper vs polystyrene foam and amount of insulation affect the accuracy? Are you going to do it electrically? If so, won't the resistor heat up and change resistance as the experiment progresses; are you using a stable DC source or a unfiltered rectified AC source from a lab power supply that is bumpy (see diagram below)? This may affect your voltmeter reading and the calculation of energy transferred:

·     Investigate the resistivity of different types of graphite
Carbon composition resistors are made from a molded carbon powder that has been mixed with a phenolic binder to create a uniform resistive body. It is then surrounded in a insulating case after attaching end leads. The greater the % carbon the lower the resistance. You could model a resistor using graphite 'lead' pencils. It is the pencil-makers' policy not to reveal the %carbon in their pencils but I have it on good authority that 9B is 25% clay and 75% graphite and this changes in equal steps to 9H which is 75% clay and 25% graphite. For an EEI you could measure V vs I for 4B through to 4H pencil graphites; what's the difference (% clay?). How does diameter affect result?

·     How high will water syphon?
Use clear plastic tube 20 m long in U-shape; effect of boiling water first; effect of temperature. Is the density of the liquid the main factor or is vapour pressure or intermolecular force a factor?

·     Investigate the coefficient of friction for accelerating surfaces
For sliding friction on an incline, the coefficient of friction μ = tan θ for constant speed; but if the block is accelerating life is not so simple. You could investigate friction for objects being shot up an incline and coming to rest (what to vary, what to control?). What about the motion of a block of wood resting on top of a piece of wood that is oscillating back and forth?

·     Egg cooking
The yolk and white of an egg have different thermal conductivities so I’m told. So how does the temperature rise of the two parts of an egg compare when it is being boiled. Much work has been done on eggs but maybe not on this. I’d say you’d need the temperature probes and a lab interface of some sort.

·     Investigate the ballistic pendulum
(does accuracy in measurement of speed vary with speed of projectile; what is the optimum mass of the pendulum bob (plasticine) and string length for different speeds or momenta?)

·     Investigate the absorption of sound at different frequencies
In the music rooms at Moreton Bay College there are large sliding panels hanging from the wall. One side of the panel is covered with a loop-pile carpet, the other side has cork. I asked the architect why he did this and he said so they could 'tune' the room and remove annoying frequencies. You could do an EEI to investigate the sound deadening effect of different substances. How does % absorption vs thickness; vs frequency; vs loudness. What relationship is there with density of the sound absorbing barrier?)

·     Meniscus shape
Think of how many times your teacher has cautioned you to "read to the bottom of the meniscus" when you're using a measuring cylinder, pipette or burette. A characteristic of liquids in glass containers is that they curve at the edges. This curvature is called the meniscus. Think of how many times your science teacher warned you to read to the bottom of the meniscus when reading measuring cylinders and so on. How does the meniscus angle change with temperature, type of liquid (eg various alkanes), density.

·     Construct and investigate a simple, tuned musical instrument
Which harmonics are emphasised (odd/even); factors affecting the sound envelope (attack, sustain, decay); how can you modify your instrument to increase the range of frequencies both higher and lower? As a start, I've measured a school xylophone but removed some of the key dimensions.

·     Investigate the speed of sound in air
It is said that the speed of sound increases by 0.6 ms^-1 for every degree Celsius rise in temperature. But is this accurate over a wide range of temperature change? You could investigate: speed vs temp; vs humidity; speed in different gases (different densities, molar masses). Or how does it vary from a day of high pressure (eg 1020hPa) to a low pressure day (eg 995hPa)?

·    Self-inductance in a solenoid
Consider the circuit below (left). Nothing happens to the brightness of the bulb when the metal rod is inserted into the coil. But if you use the circuit on the right where the source of power is an alternating current, insertion of the rod affects the brightness. This illustrates the property of self inductance. As a consequence of this, when a DC supply that is connected to a solenoid and is switched on, the current doesn't respond immediately. The same is true when the circuit is switched off. You could investigate the effect of different metal bars, coil size, size of AC etc. A CRO may be better than a bulb for getting quantitative data.

·     Molecular sizes of gases
You know how helium balloons deflate rather quickly as the gas leaks through the porous rubber? Well, a hydrogen balloon deflates even quicker as it's molecules are even smaller. You would think that the rate of deflation would somehow vary with the molecular size.

·     Investigate the factors affecting the resistance of a resistor
You could measure resistance vs temperature; linearity with increasing voltage. Solder wires on to each end, wrap it in GladWrap and put in a test tube (with a thermometer) and place in a beaker of water to be heated. Try different resistances. Can you get some dry-ice; how about getting some liquid nitrogen (under supervision)?

·     Measure the audible range of a human being
You could measure frequency range, loudness; may be able to get access to audiologist's equipment; variation with age, sex, occupation; test family and friends. But how do you stop it being so subjective. Where does the physics come in?

·     See-Saw with Ball
You can set up a grooved piece of wood on a knife-edge (like a see-saw) and place a ball on one side. When released the balance tips and the ball rolls back. You could investigate the force vectors for getting it to maintain a back-and-forth oscillation. Cool!

·     Wing lift
One of the things keeping a plane in the air is lift. Lift is produced by a lower pressure created on the upper surface of an airplane's wing compared to the pressure on the wing's lower surface, causing the wing to be "lifted" upward. The special shape of the airplane wing (airfoil) is designed so that air flowing over it will have to travel a greater distance faster, resulting in a lower pressure area (see illustration) thus lifting the wing upward. Lift is that force which opposes the force of gravity (or weight). You could make models of wings and place them in front of a fan. Vary the attack angle, shape and so on. Clue: read up on The Coanda Effect.

·     Investigate the interference of sound waves
Can a wave be superimposed on another to cancel out the sound? This is what they do in noise-cancelling headphones and car interiors. Maybe too complicated for an EEI but you could look at interference of waves between two speakers and measure the degree of cancellation (but how to minimize reflections off the walls?).

·     Rate of cooling and surface area
An interesting EEI can be made from filling balloons of different sizes and shapes (cylindrical, spherical) with hot water and measuring cooling rates in a gentle forced breeze. You can look at shape and surface area.

·     Transformers and power losses
Electrical transformers are used to "transform" voltage from one level to another, usually from a higher voltage to a lower voltage. A changing current in the first circuit (the primary) creates a changing magnetic field; in turn, this magnetic field induces a changing voltage in the second circuit (the secondary). Transformers are some of the most efficient electrical 'machines', with some large units able to transfer 99.75% of their input power to their output. Your EEI could be about the factors that influence the power losses. Is it frequency, voltage, current or just what? What ever you do, don't use mains (240V) voltage. Use the school's laboratory power pack or a signal generator.

·     Perpetual motion machines.
Now we know they can't work but trying to figure out why they can't work is a bit harder. You could make a few models from designs on the internet and work out what they don't work. You'll need some estimate of % efficiency and that might be hard to gather.

·     Variables that affect drag forces in boats.
The "Hull Speed" is the maximum speed before drag increases dramatically. For a 30m ship it is about 24km/h; for a 30cm duck it is about 2.4 km/h. There's lots to test and talk about there. I'm guessing it's all to do with the ratio of surface tension to hull area. Variables: drag vs speed; length; width; shape.

·     Switching from walking to running
Prof. McNeill Alexander from Leeds University (UK) developed Alexander's Rule which says that v² = gd_H/2 (where d_H is the distance from hip to ground) that shows the speed at which an animal switches from walking to running and this is supposed to work for insects to humans. But I'm not so sure! How could you do an EEI on this? Better get good advice from your teacher before you start.

·     Controlling the speed and direction of sailboats
Hint: collision trolley, sail, electric fan, spring balance; wind force vs angle, speed of wind, area of sail; say no more!

·     Does pyramid power really work?
What possible forces; size of pyramid, material, angles, what to test (freshness of eggs?); is this really science?

·     DC Motor
What factors affect the rotational speed of a simple DC motor. You'd think that as you increased the voltage it would just get faster and faster, but alas, a thing called "back EMF" spoils the party. What factors are involved here?

·     To determine if Mersenne’s law of stretched springs applies to slinkies.
Well why shouldn't it; it is the same principle. But how do you minimize friction. And what about the heavy spring: snaky?

·     To investigate the factors which affect the specific heat capacity of various concentrations of salt water solutions.
In a lot of questions you are told to take the specific heat of a solution (seawater, milk) as being the same as distilled water. But is this fair? Maybe some of the heat is used to increase the vibration of the hydrated Na⁺ and Cl^- ions. But wait - 100 g of salt water has a smaller volume than 100g distilled water so maybe......

·     To measure the specific latent heat of vaporisation of liquid nitrogen.
The specific latent heat of vaporisation of water is not such a big deal - it has been done to death by physics students in laboratories all over the world for the past 140 years. But this is an EEI and critical thinking has to be applied. That's why nitrogen could be tried. Liquid nitrogen is not easy to get hold of or store, and even less easy to handle. Doctor's surgeries often have it to freeze off warts and skin cancers so maybe there's a clue. It wouldn't be easy but with teacher guidance this could be a great EEI.

·     To determine the effect of changing temperature on the viscosity of honey.
Have you ever tried to eat honey that has been in the refrigerator - hopeless huh? Both the viscosity and the density of honey change with temperature and water content and I'm told the viscosity and temperature follow a inverse cube relationship. Honey is mostly sugar (glucose/fructose and water). Thus the two variables seem to be temperature and moisture content. But how will you control moisture, and how will you measure viscosity (maybe a ball bearing - but what size and what about the diameter of the tube - is there viscous drag)?


·     Can a pendulum predict the sex of a chicken while it is in the egg?
Is this really physics?; what forces are acting?; who thought of this? You'd have to be very confident or plain daring to choose this for an EEI.

·     Can eggs stand more force from some directions?
Build a pressure gauge; can it be connected to a TI-CBL or computer; what is the hypothesis?. Does cooking (for how long) affect this?

· How strong is human hair of different thickness?
For a healthy individual with no hair diseases, hair fibre is very strong with tensile strength around 1.6 x10-9 N m^-2. That makes hair about as strong as copper wire of the same diameter. So as you can see hair is incredibly strong. It also has elastic properties. It can stretch up to 20% of its original length before breaking when it is dry and when it is wet it may stretch up to 50% before breaking. But do you believe the ads that say their products can improve the strength of hair (see the one below). Sounds a bit far-fetched to me. You could measure elongation vs weight; breaking strength vs diameter; vs colour; are different colours more stretchy (how to control variables?); effect of humidity, heat, prolonged light, age of subject and so on.

· How strong are nylon fishing lines?
Platypus is Australia's leading and oldest brand of fishing line. One of their ads said: "Platypus Super-100™ has been crafted using a new process, allowing an outer skin to be toughened while the core remains supple and flexible. An advanced coating is also applied to the line for added abrasion resistance. Platypus Super-100™ is fast gaining a reputation as the only choice for serious anglers, both as mainline and as tippet. Platypus has spent many years perfecting the resin blend and fine tuning their production methods to bring Super-100™ to you". Does this sound like a lot of advertising hype? Perhaps you could try different brands and measure strength vs diameter; or another variable. What is the hypothesis going to be?

· Which truss design supports the most weight?
You've probably noticed how bridges seem to be made up of lots of triangles (or 'trusses'). In architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight slender beams whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and result in forces in the beams which are either tensile or compressive forces. You could investigate how a paddlepop stick truss reacts to a load added to the top. You could reduce the thickness of a beam and see if it affects the load capacity before it breaks.

·     Which beam design makes the strongest truss?
As a continuation of the above suggestion, you could combine a couple of trusses and see how they then react to the loads. After all, in the middle node at the bottom, tension now becomes compression.

·     How strong is silkworm silk?
Silk is a continuous filament fibre consisting of fibroin protein secreted from glands in the head of each silkworm larva and a gum which cements the two filaments together. To make useful thread for clothing, the raw silk is twisted into a strand sufficiently strong for weaving or knitting. Four different types of silk thread may be produced from this procedure: crepe, tram, thrown singles and organzine. Crepe is made by twisting individual threads of raw silk, doubling two or more of these together, and then twisting them again. Tram is made by twisting two or more threads in only one direction. Thrown singles are individual threads that are twisted in only one direction. Organzine is a thread made by giving the raw silk a preliminary twist in one direction and then twisting two of these threads together in the opposite direction. How does the strength of the four methods compare? What's the hypothesis? You can get cocoons from ebay for $12 including postage for 33 cocoons. Posted from the Sunshine Coast, Queensland.

·     The effect of light on degradable materials
Biodegradable plastics are seen by many as a promising solution to the problem of single-use conventional plastic bags. Although there are a variety of degradable plastics which may assist reducing the resource wastage and litter problems associated with plastic shopping bags, there is unfortunately no easy solution. Degradability is the ability of materials to break down, by bacterial (biodegradable), thermal (oxidative) or ultraviolet (photodegradable) action. If you can get hold of a degradable plastic bag you could test the thermal and photodegradable properties by measure the breaking strain before and after treatment. Is the wavelength important, or is it just the intensity? Is temperature important, or just time? A great EEI and so useful too.

·     Polarisation of light in acidified sugar solution
Certain materials (sugar in this experiment) are optically active because the molecules themselves have a twist in them. When linearly polarized light passes through an optically active material, its direction of polarization is rotated. The angle of rotation depends on the thickness of the material and the wavelength of the light. You could make up a solution of sugar (sucrose) and hydrolyse it using dilute acid. As the reaction proceeds, the degree of polarisation changes and this can be observed using crossed polarisers either side of the solution placed on an OHP. You could look at the effect of angle vs. concentration vs time; depth effects; acidity effects; temperature.

·     Comparing the strength of laminated and unlaminated wood beams
Make your own plywood out of paddlepop sticks. How does breaking force or deflection vary with number of sticks? Turn the beam on it's side and try again.


·     How do different woods expand when they are wet?
In which direction do they swell (if at all)? Is it a linear function with % moisture? If they swell, do they become more or less dense? What physics principles are being tested?


Red hot - the ball bearing just sits there	...and then takes off as it cools	and smashes into the end at high speed.