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Topic 7: Fluid Pressure . What is Pressure? . PRESSURE is a measure of the force acting perpendicular to a unit area Pressure can be calculated by using the following formula: . The unit for pressure is newtons per square metre or a pascal (Pa) 1000 Pa = 1 kPa.
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What is Pressure? • PRESSURE is a measure of the force acting perpendicular to a unit area • Pressure can be calculated by using the following formula:
The unit for pressure is newtons per square metre or a pascal (Pa) • 1000 Pa = 1 kPa
Watch the following clip of a how to build a COMPRESSED AIR ROCKET http://www.youtube.com/watch?v=eNFfK5uo6D0
Compression of a Gas • These three requirements are needed for a compression of gas • The gas must be enclosed in a sealed container with sturdy walls (in this case it’s the pressure chamber made out of tubes) • There is so much space between the particles • An outside force is applied to the gas to push the particles closer together (in this case it’s the pump, which forces air into the chamber)
We say that gas is COMPRESSIBLE because their particles can be squeezed together closer together • Although there are spaces in between particles of solids and liquids, the spaces are as small as possible. We say that solids and liquids are INCOMPRESSIBLE
Another useful property of gases is there ability to exert a force back (counterforce) when they are compressed • Consider the tires in your car • When a car drives on a bump, the tire compresses the air and transfers the force all over the tire instead of the body of the car
Atmospheric Pressure • Just as water pressure changes with depth, air pressure changes with altitude • As you climb higher, there are fewer air particles pressing against you. (lower air pressure). • The air pressure inside of you still remains the same as you are climbing and changes slowly. That’s why you hear a popping in your ears
Measuring Air Pressure • Air Pressure is measured by a BAROMETER • Liquid mercury is found in a glass tube standing upright at the bottom is a pool of liquid mercury • When the air pressure increases, the mercury is pushed down, causing the mercury inside the tube to go up
Balanced and Unbalanced Forces • If the inside of a closed container has a lower air pressure pushing on the outside, the walls of the container will buckle and cave in. • The lower air pressure inside and the higher pressure outside create an UNBALANCED FORCE. The force from outside the box pushes the container inward.