LEARNING OBJECTIVES

Knowledge of subject matter

- Define pressure as the perpendicular force acting per unit area.
- Solve problems involving pressure.
- Describe applications of Pascal's principle.
- Explain why objects float or sink in water.
- State Archimedes' principle of flotation.
- Define density and specific gravity. Solve problems involving density.
- Explain what a hydrometer is.
- Explain how hot–air balloons, ships, fish and submarines are able to float or sink.
- State the pressure–depth relationship of fluids. Solve problems involving pressure and depth.

SCIENTIFIC PROCESSES

- Design simple experiments to test predictions about flotation.
- Identify issues involving underwater safety.
- Gather first hand data on vehicle forces on roadways.
- Describe relationships between air pressure and altitude from given data.

COMPLEX REASONING

- Solve challenging problems on forces and fluids.
- Use creative thinking to solve perplexing puzzles about pressure and buoyancy.

- Hydrostatics is the science of fluids at rest.
- A fluid is a substance that can flow. It offers no permanent resistance to deforming forces. Fluids include liquids and gases. Viscosity is a measure of the ability to flow.
- Density = mass per unit volume.
- Pressure is defined as force per unit area, the force being at right angles to the force. It is measured in pascal (Pa).
- The gas particles of the atmosphere have weight and they exert a pressure on us and the surface of the earth. At sea level normal atmospheric pressure is 101.325 kPa.
- Three common ways of measuring air pressure are with the barometer, the manometer and the Bourdon Gauge.
- The gauge pressure is the pressure of a fluid relative to atmospheric pressure.
- Blood pressure is measured with an instrument called a sphygmomanometer.
- Pascal's principle: Pressure applied at any point to a fluid in a closed vessel is transmitted equally to every other point in the fluid.
- Applications of Pascal's principle include the hydraulic car jack and the hydraulic hoist: P = F
_{1}/A_{1}= F_{2}/A_{2} - Archimedes' principle: when an object is wholly or partially immersed in a fluid, the upthrust on the object is equal to the weight of the fluid displaced.
- The specific gravity (SG) is defined as the ratio of the mass of an object in air compared with the mass of an equal volume of water.
- The density of a solid floating in a fluid is equal to the density of the fluid times the fraction of the volume submerged.
- The hydrometer is a device for measuring the specific gravity of electrolytes, antifreeze solutions, milk, alcohol and other liquids.
- Ships have special marks on their side to show how deeply the fully laden ship could safely float in different kinds of water. The mark is called the Plimsoll line.
- Pressure increases with depth in a fluid: P = rgh (where r = density).