Chapter 3 Section 3 – Gas Behavior A Fluid is any material that can flow and that takes the shape of its container. Fluids include water and oil, and gases such as oxygen and carbon dioxide. Fluids are able to flow because the particles in fluids, unlike the particles in solids, can move easily past each other. The amount of force exerted on a given area is pressure. For example, pumping air into a tire. The formula for how we calculate the amount of pressure being exerted on an object is as follows: Pressure = Force / Area Pressure is measured in SI units called pascal. (Pa)

Let’s Try some problems calculating Pressure, Force, & Area. Find the pressure exerted by a 3,000 N crate with an area of 2m squared. Pressure = Force / Area 3,000 N / 2m = 1,500 Pa Find the weight of a rock with an area of 10m squared that exerts a pressure of 250Pa. 250Pa x 10m = 2,500 N

The atmosphere extends as far as 150km above us. The atmosphere is the layer of nitrogen, oxygen, and other gases that surrounds the Earth. The atmosphere extends as far as 150km above us. The pressure caused by the weight of the atmosphere is called atmospheric pressure. Atmospheric pressure is exerted on everything on Earth, including us. Earth’s atmosphere is held in place by gravity, which pulls the gases toward Earth. Atmospheric Pressure is different depending on where you are in the world. For Example, the pressure is different on Mt. Everest than in Troy, NY. http://www.pbs.org/wgbh/nova/everest/exposure/pressure.html

Water pressure increases with depth because of gravity. The deeper the diver goes in the water, the greater the pressure becomes because more water above the diver is being pulled by Earth’s gravitational force. For example, a swimmer would feel the same pressure 5m below the surface of a pond as they would 5m below the surface of the ocean.

Density makes a Difference Remember Density is the amount of mass per unit volume. Because water is more dense than air, a certain volume of water has more mass, and therefore weighs more than the same volume of air. Therefore, water exerts more pressure than air. Icebergs are comprised of water that has frozen, similar to ice cubes in a drink. The density of the ice is slightly less than water, causing them to float. Roughly 9/10 of the iceberg is below water.

Chapter 3 Section 3 continued Gas under pressure Pressure is the amount of force exerted on a given area. Boyles Law: For a fixed amount of gas at a constant temperature, the volume of a gas increases as its pressure decreases. Likewise, the volume of a gas decreases as its pressure increases. Charles’s Law: states that for a fixed amount of gas at a constant pressure, the volume of the gas increases as its temperature increases. Likewise, the volume of the gas decreases as its temperature decreases.

Fluids flow from High Pressure to Low Pressure When you drink from a straw, you remove some of Air in the straw. Because there is less air, the pressure In the straw is reduced. Pascal’s Principle Pascal’s principle states that a change in pressure at Any point in an enclosed fluid will be transmitted equally To all parts of that fluid. Devices that use liquids to transmit pressure to from one point to another are called hydraulic devices.

Hydraulic devices use liquids because they cannot be compressed, or squeezed, into a smaller space. This property allows liquids to transmit pressure more efficiently than gases which can be compressed a great deal more. For example, the brakes of a car of a forklift.