CHAPTER 7 Hydrostatics: The physics of fluids (Forces and Fluids).

• 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.

CHAPTER 7 SUMMARY

• 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 = F₁/A₁ = F₂/A₂
• 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).

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