Extra Critical Thinking Questions, Puzzles, experiments (and other things that didn't fit).

The numbers refer to the page numbers

3

PHYSICS FACT

The definitions of the SI base units are as follows:

Current: one ampere is the current which, if maintained in straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in a vacuum would produce a force between them of 2 x 10-7 N per metre of length.

Time: one second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

Temperature: one kelvin is 1/273.16 of the thermodynamic temperature of the triple point of water (approx. 0C).

Amount of substance: one mole is the amount of substance that contains as many elementary entities (molecules) as there are atoms in 0.012 kg of carbon-12.

Luminous intensity: one candela is the luminous intensity of a source of light that emits monochromatic radiation of frequency 540 x 1012 Hz with a radiant intensity of 1/683 watts per steradian.

Length: one metre is the length of light travelled by light in a vacuum during a time interval of 1/2999,792,458th of a second.

Mass: one kilogram is the mass of the international prototype kept in Sèvres, France.

4

NOVEL CHALLENGE

Complete the following series: 2, 3 5, 8, . If you said 12 that was the “correct” answer. But other answers are just as correct. If you recognised the numbers as the Fibonachi Series you’d get a different answer. What answer would you get and can you find anything in physics to which this series applies? One of the maths teachers said his answer was the convergents on the 5th root of 5 whatever that means.

5

INVESTIGATING

A colleague said that there are no clocks in Las Vegas gambling casinos. He thought it might be because the electrical signals interfered with the gaming devices. What’s the real reason?

9

NOVEL CHALLENGE

Write a five-minute video for TV explaining why we use newtons instead of pounds in physics.

11

PHYSICS FACT

Mathematicians will say this is a maths fact. Zero was invented by the Sumerian culture in Mesopotamia about 5000 years ago. They used a slanted double wedge // to indicate the absence of a number in a specific place. Up until then, if you had zero cows then you wouldn’t be going around talking about it. It was when the merchants arrived that zero got the nod.

18

PHYSICS FACT

Accuracy and precision are often used to mean the same thing. But they don’t: accuracy refers to how close a measured value is to the accepted value, whereas precision refers to the spread of results. For example if you made three measurements of the acceleration due to gravity and obtained 6.5, 6.6 and 6.5 m s-2 your results wouldn’t be accurate as the accepted value is 9.81 m s-2; but they would be precise as they didn’t vary much. If another group got 8.8, 9.0 and 10.8 m s-2 they would be accurate (average 9.8 m s-2) but not precise as they varied a lot.

26

NOVEL CHALLENGE

Why don’t car manufacturers put digital speedos in cars? They use analog ones. How old fashioned – or is it?

27

NOVEL CHALLENGE

The word displacement comes from the Latin dis = ‘away’, and plicare = ‘to scatter’. What about the words distill and dissect – where do they come from? And why do some people pronounce dissect as di-sect?

32

NOVEL CHALLENGE

Is it possible to have an s vs. t graph that is a circle? How about an s vs. v graph that is a circle?

32

NOVEL CHALLENGE

Draw an s vs. t graph of a plane that has taken off from Brisbane airport in a straight line to Cairns but it had to circle above the airport three times before landing.

32

NOVEL CHALLENGE

Some people say that premium unleaded petrol is more economical as you can go further on a tank-full. If regular unleaded petrol was 80 c/L and a car used 15 L/100km, how many L per 100 km would it have to get out of premium unleaded at 90 c/L to be worthwhile?

34

NOVEL CHALLENGE

Sketch an s vs. t graph of your wristwatch as you walk along a street.

34

INVESTIGATING

Watch a champion swimmer and note the displacement of the hand. As the hand goes back the body moves forward. Is the displacement of the hand relative to the pool bottom positive or negative during the stroke? Draw an s vs. t graph of the hand during a 50 m race and during a 100 m race (two laps).

43

INVESTIGATING

Hold a TI Ranger about 30 cm above a bench top and let a ping pong ball bounce underneath. You should get a good value for ‘g’ from the slope. We get about 9.7 m s-2. How could you improve the accuracy?

66

NOVEL CHALLENGE

It is hard to say when graphs were invented. There is some evidence that they were used 2000 years ago but it was Galileo in the 1600s who plotted the times and distances for a ball rolling down various slopes. Why is the x-axis called the abscissa and the y-axis the ordinate? What would a time vs. speed graph look like for a plane doing a loop-the-loop?

68

PHYSICS FACT

The word exponential comes from the 16th Century Latin ex = ‘out of’ and ponere = ‘to place’. Hence the exponent is written ‘out of place’ or above the number.

69

NOVEL CHALLENGE

The number of transistors that can be placed on an integrated circuit is increasing by 20% per year. Is this exponential or linear or something else?

69

NOVEL CHALLENGE

Stock market analysts often take a heap of share price data over a long period of time and find a mathematical formula to fit the data. Physicists do the same. Does this make stock market analysis a science? What else is needed?

81

INVESTIGATING

In a car accident where a person’s head is involved (e.g. hitting a tree through a side window), is it better to have the skull crack or stay intact? What is the physics principle behind your answer?

82

NOVEL CHALLENGE

The Space Shuttle has a total mass at lift-off of 2000 tonnes. It has three main engines each of which develop 1.668 MN of thrust. How many seconds after lift-off will it have reached escape velocity of 11 km per second?

86

PHYSICS FACT

Mass can also be thought of as the amount of matter in a substance. That’s probably what you learnt in Year 8. It is true though - the more protons and neutrons a substance has the bigger its mass. But it’s not the official definition – it is more a logical consequence.

88

NOVEL CHALLENGE

Imagine you are standing on some bathroom scales which are placed on top of a trapdoor. If the trapdoor opens what happens to (a) the scale reading; (b) your weight; (c) your mass; (d) the distance between the scales and your feet (initially zero)?

88

NOVEL CHALLENGE

On a weight loss show on TV, one man had a mass of 200kg and he said he had to go to the post office to get weighed. Why couldn’t he just stand on two scales with one foot on each? Why couldn’t he put one set of scales on top of the other and stand on the pair?

89

INVESTIGATING

Stimulus for an EEI: what factors affect parachute descent; canopy area, mass, apex vent size, number of lines, shape of canopy?

91

NOVEL CHALLENGE

Mr Crackles was a baby pig that was picked up by an eagle in New Zealand in September 2003. The eagle took him to an altitude of 900 m and let him fall. Eagles do this to kill their prey. Mr Crackles was a small black furball the size of a football who landed on a bitumen roadway and ran away. He was the star of the TV news that night. Mr Crackles fell the 900 m in 50 seconds. Estimate his drag coefficient?

92

NOVEL CHALLENGE

In Volume 33 page 523 of Applied Ergonomics, they measured the force needed to drag a sheep along different surfaces. They concluded that it was easier to pull a sheep down an incline than on a level surface (duh!). This hardly seems surprising to us physicists but the good folk at Applied Ergonomics are probably mathematicians. At what angle will the force required be 50% of the force on a horizontal floor? If you had to pull the poor old sheep UP the same incline would the force be double the horizontal value?

93

NOVEL CHALLENGE

The etymology of the word tension is that it comes from Middle French tendere = ‘to stretch’. Is this also used in the words tendon, tensile, tentacle, tennis, tenant, tense, tent?

98

PHYSICS FACT

A new carbon-based ceramic compound is being used to make pistons in German steam engines. It has a coefficient of friction of 0.008 and that’s low!

100

NOVEL CHALLENGE

An enthusiastic young car owner loved dragging off others at the traffic lights. But he wanted to make his car go faster. He installed a more powerful engine but the wheels spun too much at take off. He wanted to increase friction and he knew that it was proportional to mass so he put a few bags of sand in the car. Would this help?

102

INVESTIGATING

Stimulus for an Extended Experimental Investigation (EEI): what factors affect the descent rate of a ball bearing in a liquid: mass, volume, viscosity? How are they related? What theory underpins this experiment? In 1851 physicist George Stokes developed Stokes’ Law (v = 2gr2(d1-d2)/9). Try it for yourself. However, German physicist Wilhelm Roentgen thought there must be some viscous drag from the walls of the tube if the ball was big. So what happens when the ball diameter and the tube diameter are similar?

109

PHYSICS FACT

The first “thought” experiment ever carried out in the name of science was by Galileo Medici who wondered what the path of a ball would be if you dropped it off a running horse.

111

NOVEL CHALLENGE

The etymology of the word range is that it comes from the Old French rangier = ‘to place in a row’. Does this have anything to do with a forest ranger?

125

NOVEL CHALLENGE

In Star Trek they talk about inertial dampers. What are they and how do they work?

129

NOVEL CHALLENGE

Galileo was 17 years old when he watched the lanterns swing in the Cathedral of Piza in 1581. He said he was glad he was not born in a leap year. When was he born?

145

NOVEL CHALLENGE

Astrobiologists have been searching the skies for evidence of life but have come up with mixed results. The problem is that they can’t define ‘life’. International committees have debated the problem for years and it’s getting worse. Ask a biology student and see what they say. Physicists were faced with a conundrum once: how to tell someone from another galaxy which way was left and right. They solved that once ‘non-conservation of parity’ was discovered. What’s that?

148

INVESTIGATING .

Physicists believe that the value of the gravitational constant (G) may be affected by the Earth’s magnetic field. One team of researchers calculated the value to be 6.6699  0.0007 x 10-11 at the Tropic of Cancer and another team calculated it as 6.67559  0.0003 x 10-11 at the Equator. Have a look on the Internet – which value is most accepted?

154

NOVEL CHALLENGE

Physicists have made a gravimeter that can detect changes in gravity of one part in a million. It is being used in mineral exploration to detect underground diamond “pipes” from a plane flying at 185 km h-1 at an altitude of 90 m. These pipes have a density of about 10% of the surrounding bedrock. It can even detect the gravitational field of a two-year-old child at two metres. Calculate how far the child would have to move to change the force by 1:106.

157

NOVEL CHALLENGE

How would you know if a Black Hole was on a collision course with Earth. You wouldn’t know until it hit because you couldn’t see it. Some physicists believe that a Black Hole may have come close to our Solar System hundreds of millions of years ago and pushed the comets towards Earth where they crashed and wiped out the dinosaurs. You could detect it if you shone a powerful laser at it because the light would be bent around the back of it and come back to Earth. Why would this happen?

167

INVESTIGATING

Take a fresh chook’s egg between your hands and place so that the pointy ends are touching your palms. Squeeze as hard as you can and you won’t be able to break it no matter how hard you press. Why is this? Don’t turn the egg sideways or you’ll be very sorry.

169

PHYSICS FACT

Other units for pressure and their conversions are: 1 atmosphere (atm) = 101.3 kPa = 760 mmHg = 15 pounds per square inch (psi). Homework question: well then what’s a torr?

169

INVESTIGATING

Measure your blood pressure after you run, walk, sleep. Subtract the diastolic from the systolic to get the mean pressure. How is this related to pulse rate for these activities?

170

INVESTIGATING

We’ve always wondered how the grade of oil relates to its viscosity. For example: is 10W30 three-quarters the viscosity of 10W40 at the same temperature?

172

INVESTIGATING

Here’s a good investigation: the physics of buoyancy and sail boating. You could determine variables that affect buoyant forces along with factors involved in controlling the speed and direction of sailboats.

173

INVESTIGATING

How much does your head weigh? Anatomists have measured heads removed from bodies and have found they have an average mass of 4.5 kg. But how could you do this without decapitation?

185

NOVEL CHALLENGE

Why does a boxer stand with his feet apart?

188

NOVEL CHALLENGE

An exam favourite. A 200 gram cricket ball travelling at 25 m s-1 north is hit east over the head of the square leg umpire at a speed of 30 m s-1. Calculate the change in velocity and momentum. Careful now - the directions are at right angles.

195

INVESTIGATING

Stimulus for an EEI: ever tried jumping off a chair with a cup full of water in your hand. What do you do to minimize the loss of water? Predict this in advance then try it. Place a few markers (pieces of tape) on various parts of the body (knee, hips, shoulder, elbow, hand) and describe the motion. A videotape would be good here. Try other people. Does practice help?

203

NOVEL CHALLENGE

Structural engineers calculated that the torque produced by the impact of each of the hijacked planes that crashed into the Twin Towers on September 11, 2001 as 7.7 million foot tonnes. The maximum torque that each tower was designed for was 7.4 million foot tonnes but because the buildings flexed and absorbed the energy they didn’t collapse as a result of the impact. Convert these values to the SI unit for torque (1 tonne = 1000 kg; 1 pound weight = weight of a one pound mass; 1 kg = 2.20 pounds of mass). Don’t you just love the old imperial system of weights and measures? They also have dynes, poundals and slugs for force.

204

INVESTIGATING

When you knock toast off the kitchen bench it does a flip and lands butter-side down. The moment of inertia and the distance conspire to make this happen. But if you give it more time to fall it should land butter-side up. Try it off the top of a refrigerator. You’ll be amazed – we were. What factors affect the rotation? If you strapped a piece of buttered toast to the back of a cat and the cat fell off a table, which way would it land?

204

INVESTIGATING

Stimulus for an EEI: Roll some golf balls down an incline. How does the rate compare to what they are made of? Why are some faster than others? Cut a few open (don’t tell Dad).

207

INVESTIGATING

Stimulus for an EEI: are momentum and kinetic energy conserved in billiard ball collisions. Why not get two CBL2s and light gates and investigate this at your local pool hall? How does topspin, left- and right-english and backspin affect the collision?

214

INVESTIGATING

Stimulus for an EEI: How does the velocity of an arrow vary with the draw of a bow? How can you maximize distance by varying angle and tail fletch? Does 45 give maximum range (we think not)?

215

INVESTIGATING

Stimulus for an EEI: have you ever watched fun-runners pick up plastic cups of water from tables on the side of the road. It is amazing how they can grab a cup on the run and not lose any water. The cups are soft so they can’t squeeze too hard and they have to accelerate the cup slowly otherwise the water will slosh out. We don’t reckon you could program a robot to do what a brain-fried fun-runner can do automatically. Videotape some of them and see how it’s done. Explain the physics behind that.

226

NOVEL CHALLENGE

In 1895, at the Coney Island amusement park New York, they had a loop-the-loop ride but people kept getting whiplash and breaking their necks and collar bones. The engineers changed the shape from circular to elliptical. Which way would be ellipse be placed and why?

226

PHYSICS FACT

In 1902 a ride at the world mecca of amusement parks – Coney Island, New York – had a section of track removed. The cars jumped the gap and landed on the track on the other side. Sounded good in theory but breezes made it go sideways and crash. You wouldn’t have to be a genius to figure that one out.

229

NOVEL CHALLENGE

The etymology of the word perpetual is that it comes from the Latin perpes = ‘lasting’. Does this have anything to do with perpendicular, perplex or perpetrate?

229

INVESTIGATING

Stimulus for an EEI: you can measure the speed of a projectile by firing it into a target suspended on a string. This is called a ballistic pendulum (see page 227). Students have tried firing arrows into cardboard boxes hanging from the soccer goal posts but without much success. Can you design a better investigation?

229

INVESTIGATING

When designing amusement park rides, engineers prefer to use geared movement rather than freely rotating systems. The problem is that freely rotating systems can begin to resonate and speed up uncontrollably. Can you find any of this type at your amusement park?

230

INVESTIGATING

Stimulus for an EEI: optimise a water rocket. This is the sort made from a plastic soft drink bottle half-full of water and pumped up by air from a hand pump of electric tyre pump. It is messy but oh so much fun. There are a few Internet pages to give you help.

232

INVESTIGATING

Stimulus for an EEI: how well does Hooke’s Law apply to a rubber band under repeated stretch and relax? What’s going on here? Do metal springs follow the same pattern? If not, why not?

233

INVESTIGATING

Stimulus for an EEI: investigate the variables to optimise the accuracy and range for a trebuchet or a catapult. This would have been one classy investigation in a 1700s university physics class because otherwise it would be done by trial and error. There’s a lot on the Internet about this. Make one and launch some rocks (point away from the teachers’ car park).

246

INVESTIGATING

You can determine the specific heat of a metal by placing pieces of heated metal in a cup full of water and measuring temperature changes. But how does the accuracy vary with the volume of water and the mass of metal used?

252

NOVEL CHALLENGE

It is sometimes said that physicists are more interested in the race than the prize. What do you think this means? Do you think it is true?

252

NOVEL CHALLENGE

Space capsules get hot when they re-enter the Earth’s atmosphere. This is usually said to be because of the friction between the metal and the air. But this is wrong! They are heated as they plow into the atmosphere and compress the air ahead of them. Ever pump up a bicycle tire and discover that the pump and the tire have become hot? The same effect causes spacecraft and supersonic aircraft to heat up as they compress the air at their leading edges. It is called adiabatic compression. How can you prove that it is not from air friction?

258

NOVEL CHALLENGE

Ever wondered what would happen if you drank liquid nitrogen. Some idiot in the UK did and it was written up in Chemical Health and Safety journal. He collapsed in intense pain, unable to breath and passed out. Surgeons removed part of his stomach. What temperature does nitrogen boil at?

259

PHYSICS FACT

On our next trip to Italy we were going to drop in and visit Avogadro’s house – it’s been made into a tourist attraction. What do you think Avogadro’s house number is? We were bitterly disappointed to hear that it doesn’t have one. None of them in the street do. You think they’d put a 602 on the front fence.

274

INVESTIGATING

This is a beauty! You know that the energy of a photon is proportional to its frequency and hence colour (E = hf). If you created the spectrum of some sunlight using a prism and put thermometers in each of the colours, would you pick up a temperature difference? On September 11, 1800, William Herschel did just that but when he came back from morning tea the Sun had moved and the thermometer that was in the red was not in any colour. But the temperature was even higher. He thought “what the…?” The rest is history. What did he discover? What is the other side of violet? Sounds like a great EEI.

274

INVESTIGATING

In 1780, French physicist Leclerc measured the rate of cooling of a 20 cm diameter iron cannonball that was heated to white hot. Thermometers didn’t exist so he asked some young ladies with soft hands to estimate the temperature (yeah, right…well that’s his story). From this he deduced that the Earth was 50 000 years old. Someone mentioned that the Earth was also heated by the Sun so he gave a revised figure of 74 832 years. But he didn’t know about the one thing that heats the Earth up. What is that? A good EEI would be to investigate the rate of cooling of hot metals of similar mass but different shapes (and surface areas).

278

INVESTIGATING

Stimulus for an EEI: what relationship is there between the amount of insulation on a plastic bottle full of hot water and rate of cooling. You could use a 2L soft drink bottle and layers of bubble wrap. Is the “decay” curve logarithmic (y  e-kt)?

281

INVESTIGATING

Stimulus for an EEI: What is the fastest way to cool and freeze water in a freezer? Should you use a foam cup (with or without a lid), a beaker, a metal can. How will you measure temperature (we’d use a TI-83 graphing calculator and a CBL2). What physics principles underpin your result? What relationship was there with T and t?

281

INVESTIGATING

Stimulus for an EEI: do all mammals have the same body temperature, respiration rate and pulse rate. Will your dog let you put a thermometer under his arm? How are these factors related to body size? What does this have to do with physics?

281

NOVEL CHALLENGE

Clouds are heavy. Evaporated water is less dense than air, so it rises, but when the water gas condenses to form clouds, it contracts by about 800 times and turns into very dense liquid water. Even a small cloud contains tons of liquid water. How can clouds remain aloft?

282

INVESTIGATING

Insert three temperature probes in a TI CBL2 and attach to black, white and silver metal surfaces. Note the temperature change when placed in the Sun (or a light bulb but keep distance the same). Can you deduce any mathematical heating relationship.

282

NOVEL CHALLENGE

German physicist Walter Nernst inherited a farm and found that the barn was warm because of the animals in there. He got rid of them and said “I don’t want animals that are not in thermal equilibrium with their surroundings and waste money on heating the universe”. What sort of animals do you think he got instead (starts with “f”)? Nernst went on to invent the 3rd Law of Thermodynamics. Someone else trumped him with the others laws. What is the difference between the zero, first, second and third laws of thermodynamics?

295

INVESTIGATING

New Scientist magazine says that uncooked spaghetti strands always break into three pieces when dropped on to a hard floor. Now why is this? We think it is to do with standing waves in the strand and the position of antinodes. Can you test this hypothesis? Does height matter?

323

PHYSICS FACT

Physicists have passed light through a hole less than half the wavelength of the light. You’d expect a lot of diffraction but there is hardly any (about a 5º spread). It is because the hole has corrugations running around the edge and the light somehow interferes and cancels out the spreading wave. Neat huh?

330

INVESTIGATING

Japanese physicists have found that a 3 mm thick layer of a Ni-Zn-ferrite material sandwiched between thin wooden sheets makes an ideal insulator of mobile phone signals. It can reduce the signal by 97%. They use this to line the walls of concert halls so that the audiences’ phones won’t work. Mobiles work at 900 MHz and 1.8 GHz with a power of about 600 mW. A good experiment would be to test various substance for their insulating ability and develop a theory for why some work better than others. You may get a job in Japan.

338

INVESTIGATING

Use a TI CBL2 and a light probe to measure the light from an incandescent bulb or a fluorescent light. Set the sample interval at 0.001 s and you’ll be delighted with the result. You should see a 50 Hz flicker from the bulb. But what do you see from the fluoro? Now explain that!

341

INVESTIGATING

We’ve always wanted to try this but never got around to it. If you put some photographic paper in a microwave oven and turned it on, would it get exposed and come out black when you developed it. Would a computer disk lose data if you did the same thing?

341

INVESTIGATING

Stimulus for an EEI: Where are the hot spots in a microwave oven? The wavelength is 12 cm so there are antinodes every 6 cm. How to find them? Little cups of water; a cold glass plate smeared with butter; some filter paper soaked in cobalt chloride solution? How to measure quantitatively (thermometers)? The possibilities are endless.

341

INVESTIGATING

A good idea to investigate: how does the darkening of polychromatic sunglasses depend on the frequency of light. You could use some filters from the optics kits if your school has them.

345

INVESTIGATING

Stimulus for an EEI: how does the polarisation angle of light vary with time for a freshly acidified sugar solution? Why would anyone care? Answer – it’s a big deal in the sugar industry.

350

NOVEL CHALLENGE

Imagine a car that can travel faster than sound. What would you see and hear as this car approached you and came to a halt?

352

INVESTIGATING

We read in a shooting magazine that duck’s quacks don’t echo. This is scarcely believable. Why is this true?

358

PHYSICS FACT

Music composer Richard Wagner disliked fellow composer Brahms intensely. Wagner claimed that Brahms would use a bow and arrow to shoot at cats outside his window, haul them up into his room and transcribed their dying sounds into his compositions. This is not true.

359

INVESTIGATING

Stimulus for an EEI: construct a simple tuned musical instrument and play “Baa, baa black sheep”. You would need to optimise the construction so that it has a nice sound and can play the full octave required.

359

INVESTIGATION

Compare the waveform of a note from different stringed musical instruments. Look at the ‘envelope’ – the rise, the sustain and the decay. Does it depend on where the string was plucked (try the nodes and the antinodes)? You could do this with a CRO or with the sound card of your PC and suitable software. There is some good free software on the Internet.

360

INVESTIGATING

Stimulus for an EEI: sound is absorbed by various materials. One student generated a range of tones using the school’s frequency generator and found out how much energy was absorbed by connecting a microphone to a CRO. They tried different frequencies and different materials. The hard part was coming up with the physics principles to explain the results.

363

PHYSICS FACT

Want to get a great sound out of your car exhaust? If you have a V8 it will have exhaust pipes coming out of each side of the engine going down to the rear of the car. Some people have a pipe welded in between the two pipes allowing a cross flow of gases. This produces a beautiful throbbing sound from the beats.

375

NOVEL CHALLENGE

The unmanned spacecraft Luna 9 (1969) transmitted information back to Earth at a frequency of 78 MHz. When it was descending on the Moon it fired its retro-rockets and the frequency received on Earth decreased by 680 Hz. What was the new speed of Luna 9?

384

INVESTIGATING

Use a TI CBL2 and a light probe to measure reflectivity of different surfaces. Is there any relationship between the nature of the surfaces and the percentage reflectance?

389

NOVEL CHALLENGE

Paint can be glossy or flat depending on the scattering of the reflected light. There are two solids in paint that control ‘flattening’: the colour pigments and the flattening additives (such as silica). The particle size of these substances in a coating will have an effect on film smoothness, which will alter the scattering of light. Once the pigment or flatting additive has been reduced below a given particle size (10 m), the film surface becomes more uniform, thus allowing for the angle of incidence of more of the reflected light to be equal to the angle of reflection; making it more glossy. Draw diagrams to show the difference between how matte, satin and glossy paint reflect light.

391

NOVEL CHALLENGE

What is the speed of an image in a concave mirror of focal length 20 cm if an object approaches it at 2 cm s-1? Tricky – watch out!

395

NOVEL CHALLENGE

Write the text for how you would describe the image in a concave mirror to a radio audience.

409

NOVEL CHALLENGE

The Archer fish catches prey that live above the water. The fish positions itself underneath the prey sitting on a branch and hits it using a jet of water. Amazingly it can accomplish this trick even though light is refracted. Yet the Archer fish is very accurate. How can it do this?

423

NOVEL CHALLENGE

The most important characteristic of a lens is its principal focal length, or its inverse which is called the lens strength or lens "power" (P). Optometrists usually prescribe corrective lenses in terms of the lens power in a unit called diopter. The lens power is the inverse of the focal length in meters: the physical unit for lens power is 1/meter which is called diopter. For example, a 20 cm focal length convex lens has a power of 5 diopter. Question: if you double the focal length do you halve the power?

433

INVESTIGATING

The word iris comes from the Latin for rainbow; hence the word iridescent. But what has that to do with eyes or even the metal iridium?

434

NOVEL CHALLENGE

The University of New Mexico have investigated a means of correcting long sight by placing a band of electrodes vertically around the eyeball. When the electrodes are activated they shrink and squeeze the eyeball making it longer horizontally. Will this correct long or short sight? Explain.

435

INVESTIGATING

Which is better, a digital camera that has a 3x optical magnification and a 3x digital magnification; or one that has a 12x digital magnification. Define “better” and justify your assertion.

451

INVESTIGATING

Have you seen those straps that hang down from the backs of cars. They are supposed to stop the build-up of electrostatic charge on the body of the car by allowing it to leak away to earth. But they don’t work because they over look the principle of electrostatic induction on the body from the charged tyres. So what does this mean?

453

INVESTIGATING

Have you ever had a shock as you walk across a carpet and touch the windows? Carpet makers now have antistatic carpet to stop this happening. You can also get anticling spray for women’s synthetic dresses that stops them ‘riding-up’. How do these substances work? Do they additives have to be water soluble and if so, why?

475

INVESTIGATING

Stimulus for an EEI: lead pencils have a graphite core mixed with clay. Pencils with a high percent graphite (2B, 3B, 4B) are softer and more electrically conductive. Ones with a lot of clay (2H, 3H, 4H) will have high resistance and be hard. Is there any relationship between the labelling 2H, 3H, HB, B etc and the resistance? This is a really tough one. There is nothing on the Internet.

485

INVESTIGATING

Here’s a good investigation that follows on from Activity 22.5. Resistance varies with temperature, but can you verify this with the ceramic resistors as well as the wire wound ones? That’s the easy part; the hard part is relating this to theory and to try a few interesting variables. Do you have any liquid nitrogen? What happens when you put one in the Bunsen flame? Fill out a risk assessment sheet before you start this one.

490

INVESTIGATING

Stimulus for an EEI: which is the better way to heat water – in a microwave oven or in a jug? What do you mean by “better” – most efficient, fastest, cheapest, cleanest, harmless? What are some manipulated variables: time, energy, volume, power, position? What are the measured variables: time, temperature?

494

INVESTIGATING

Is it more efficient to turn off a light when you leave the room and then turning it on again when you enter, or just leave the light on? Answer – turn them off. It’s an urban legend. Now – how would you test that?

511

NOVEL CHALLENGE

The US Army is developing boots with capacitor plates in the heels. When the boot makes contact with the ground and the special elastomer heel is compressed a small charge is produced. It is enough to charge a mobile phone battery. Where does this energy normally go?

512

INVESTIGATING

Connect a 9V cell, a 1000 F capacitor and a 5.6 k resistor in parallel. Connect a TI CBL2 voltage probe across the capacitor and then remove the cell. You should get a nice discharge curve. How does it relate to theory (y = aebt)? You could make your own capacitors and test the designs. What a great EEI.

526

NOVEL CHALLENGE

How is the loudness of a sound represented on a CD? With old vinyl records it was the in the amplitude of the groove; with cassette tapes it was in the strength of the magnetisation. But for CDs, is it in the number of pits, the depth of the pit, the spacing between pits or what? This had us beaten until we thought about it logically.

556

INVESTIGATING

The magnetic inverse square law was discovered by John Mitchell. In which year was this? A long time ago Pierre Laplace speculated that if a star was sufficiently massive the escape velocity of a rocket would be greater than the speed of light. What year did he say this?

611

NOVEL CHALLENGE

New Scientist reports that an element with no protons has been discovered. It consists of four neutrons bound together and is referred to as Tetraneutron ( ) or “element zero”. Would a single neutron be an isotope of element zero or would element zero be a molecule of four neutrons? This is all very confusing and makes our brains hurt.

612

INVESTIGATING

It is hard to keep up with the newest discovered elements in a textbook. Element 110 was discovered in the late 1990s but only officially named on 20th August 2003 as Darmstadtium (Ds). A good investigation would be to compare the methods of manufacture and discovery of the transactinides (Atomic Number >103). They even think that one of the isotopes of 110 could have a half life of a billion years. We say they’re dreaming.

635

NOVEL CHALLENGE

March 1, 1954, during Operation Castle on the Bikini Atoll in the Pacific Ocean, the USA detonated the thermonuclear bomb called Bravo. It became largest thermonuclear device ever detonated by the US. During the explosion a large amount of tritium and 4He were formed because of the fast neutron fission of 7Li? What other particle must have been produced? Write a nuclear reaction. Does this make you a part of atomic testing?

637

NOVEL CHALLENGE

If a page of this textbook (80 grams per square metre) could be converted completely to energy it would be enough to raise the temperature of an Olympic swimming pool from room temperature to the boiling point. True or false?

643

NOVEL CHALLENGE

At midday, the solar energy striking the Earth is about 1 kW/m2. The radius of the Earth is 6.38 x 106 m so calculate the total energy striking the Earth (assume it to be equivalent to a flat disc facing the Sun). How much mass does the Sun burn up every second to produce this energy. Now calculate what fraction of the total energy of the Sun falls on this disc and hence calculate the total mass burnt up per second by the Sun’s nuclear reactions. We get 2.8 x 109 kg/s.

645

NOVEL CHALLENGE

“Dirty” bombs are those made from radionuclides that release dangerous radiation rather than relying on the blast effect as well. Most likely candidates are Cs-137 which is used to irradiate seeds to prevent germination and in medical treatment. In the late 1990s, a 40 g piece of material containing Cs-147 went missing from Russia. It had a 130000 GBq activity. If the half-life is 30 years, what was the concentration (%w/w) of Cs-147 in the 40g sample? Hint A = N may be useful.

645

NOVEL CHALLENGE

Here’s one for the Animal Liberationists. Ernest Lawrence was a nuclear physicist at the University of California who had element 103 named after him. To show the dangerous nature of neutrons he placed a rat in a cyclotron and irradiated it for two minutes. The rat died and everyone was shocked by how lethal this invisible radiation way. After they left, Lawrence found that the rat died from asphyxiation – lack of air – but the radiation would have killed it anyway (so he said). Just how lethal are neutrons?

690

NOVEL CHALLENGE

What is the definition of “time”? In Newton's day and up to the early 1900s, time was thought of as a background property of the universe and the same throughout the universe. But that isn’t a definition. Some people say: "Time has no definition, it just is". Others say time is “that which is characterized by the observed and apparently irreversible continuum of ordered events”. In 1910 Albert Einstein showed that time depended on who was observing it and he called this 'proper time' which varied with the observer. He defined time as "that which a clock measures". Another pragmatic definition but then you need to define a 'clock'. So how would Einstein define a clock?

695

NOVEL CHALLENGE

Physicists have sent electrical pulses down wires made of different materials and connected in series. The pulses interfere and produce beats that travel at four times the speed of light (4c). The wires used in the laboratory were 100 m long. From the beat’s perspective how long would it take to make the trip? What about from the physicists perspective standing in the laboratory?

698

PHYSICS FACT

If you ever get values of velocity greater than c then you probably have the proper quantities swapped with the relativistic quantities (eg to and t).

704

INVESTIGATING

What tests have been done of Special and General Relativity? Are there any that refute either theory? Are there any tests that have been traditionally used as confirmation of General Relativity but which can be explained by Special Relativity?

732

INVESTIGATION

Too much Sun is bad but so too is too little Sun. One problem that affects some people in winter is SAD – Seasonal Affective Disorder – also known as the ‘Winter Blues’. About 2% of people in cold climates are affected and the further from the equator you are the worse it gets. It shows up as sleep disorder, overeating, depression, lethargy and joint pain. What is the minimum amount of sunlight per day you need? How is brightness quantified? How does snow on the ground affect the incidence of SAD?

741

INVESTIGATING

Solar panels have a maximum power output at certain combinations of current and voltage (P = VI). To find the optimum V and I you could connect a 5 ohm potentiometer across a solar panel with an ammeter in series and a voltmeter in parallel and go out into the Sun. Vary the resistance and record and plot the results (V against I). What is the optimum power output and when? Another good experiment.

742

INVESTIGATING

Lambert’s Law says that the illumination of a light source on a surface is proportional to the cosine of the angle between the rays and the normal to the surface. You could use a solar module (like the sort from Dick Smith) attached to a multimeter (reading amps) and take it out into the sun. Measure the current at different angles. A good experiment.

Return to New Century Senior Physics - Second Edition Home Page