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Science 8 - Chapter 9 Pressure

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by

Timon Piccini

on 5 December 2011

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Transcript of Science 8 - Chapter 9 Pressure

Pressure Pressure is all around us Where do you see pressure everyday? We experience pressure every day Air pressure Atmospheric Pressure The earth’s atmosphere extends 500 km up, in 5 different layers. (see pg 322) Each layer presses down on the layers underneath it. Air pressure decreases as altitude increases (the higher you go, the lower the air pressure). Your ears “pop” when the pressure inside your ear becomes equal with the pressure outside. How can we use pressure? Pressure differences cause force. Fluids move naturally from an area of high pressure to low pressure. The movement of pressurized gases results in a force that we can use to do things. Ex. air compressor, scuba tanks, nail gun Ex. straw Liquid Pressure In liquid pressure: The deeper the fluid, the more pressure. Ex. For every 10 m you go down into water, the pressure increases by 1 atm!

Ex) at a depth of 500 m, each square metre of a submarine experiences the force exerted by the weight of 40 elephants! Think of a high pressure situation. Would you want to stay there? Do you feel a little fluid? On a piece of paper tell me what your high pressure situation is. 1. Why is it high pressure?
2. Why do you want to leave it?
3. How did you get away?
4. How is this like a fluid under pressure? Buoyancy With all fluids we have buoyancy. Buoyancy
The tendency of objects in fluids to rise or sink because of the density differences with their surroundings These differences in densities cause a force.

Buoyant force: the upward force exerted by a fluid

Ex) if the force downward on an object (because of gravity) is greater than the buoyant force, the object will sink. Basically the buoyant force is equal to the weight of the fluid being displaced. Buoyancy in action! • Most kinds of fish possess an organ called a “swim bladder.” A fish can control how deep it is in the water by adding or removing air from the swim bladder. The less air, the deeper the fish goes. • Submarine depth is controlled by adding or removing water. The more water, the deeper the submarine goes. • Convection is a vertical movement of fluids because of density differences.

Ex) convection currents in the atmosphere are caused when air warms, expands, decreases in density, and rise. When the air cools, it becomes more dense and sinks. Fluid Systems We all know what fluids are.. Fluids are very useful for many types of work. When we place fluids under pressure we can use them for work. There are two main types of
Fluid work...
Hydraulics and Pneumatics Hydraulics Pneumatics Haiku Showdown Create a haiku, based on one concept from atmospheric pressure, liquid pressure or buoyancy. Remember a Haiku has 3 lines
5 syllables
7 syllables
5 syllables Fluids at Rest Fluids in Motion In the 1600’s, a French doctor named Blaise Pascal studied fluid systems. He found that when you apply pressure to one part of a fluid in an enclosed system, the pressure is applied equally throughout the whole system. This is called static pressure. Fluids in motion have dynamic pressure, which is energy that can be used to perform tasks.

In the 1700’s, a Swiss scientist named David Bernoulli observed that as fluids go faster, the pressure exerted perpendicular to the motion decreases. the study of pressure in liquids •Hydraulic systems: Devices that create pressure that moves through a liquid such as oil or water. •Valves: control the movement of fluids. If they only allow fluids to flow in one direction, they are called check valves. •Hydraulic multiplication: a fluid increases and transmits a force from one point to another.
Ex) a car lift at a garage •Hydraulic systems must be carefully designed in order to minimize problems (not too many turns, large enough pipes, secure connections, etc) use gas (usually air) in an enclosed system. Gases are put pressurized using a compressor. When the pressure is released, the air particles quickly spread apart and can be used to create forces. Can lose effectiveness if the flow of air is blocked.

Ex) dirty filters prevent air from leaving a vacuum cleaner, reducing the pressure difference and making the vacuum weaker.
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