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Air and Air Pressure

Air and Air Pressure. 6C. Air is a mixture of elements, compounds and molecules that has mass, volume, and therefore density. The more molecules we put in a given volume of air, the more mass it will have. So this air will be more dense. Properties of Air. Pressure.

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Air and Air Pressure

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  1. Air and Air Pressure 6C

  2. Air is a mixture of elements, compounds and molecules that has mass, volume, and therefore density. The more molecules we put in a given volume of air, the more mass it will have. So this air will be more dense. Properties of Air

  3. Pressure • Pressure is a force that acts over a certain area. • Liquids and gases are fluids. Fluids are any material that is able to flow. Fluids exert pressure because of the motion of their particles. • Pressure will always move from a high pressure to a low pressure area. The pressure will always try to equalize. You see this when you get a hole in your bicycle tire.

  4. Air inside a ball pushes against the sides. The more air we put in a ball, the more the molecules push. So the pressure increases as we add air. Inflating example

  5. Pressure Formula • Pressure = force/area • In the SI system, we will measure force in Newtons and area in m2. This will give us pressure in Pascals(N/m2). • In our system we measure force in pounds and area in square inches (in2). This gives us pressure in pounds per square inch (psi).

  6. Review • If we increase the force, what should happen to the pressure? • It should increase. • If we increase the area over which we apply a force, what should happen to the pressure? • It should decrease!

  7. Air pressure is the result of the column of air that is above you. There is so much air above you that at sea level you have 14.7 lbs/in2 pushing on you. Air Pressure

  8. Why are we not crushed by air pressure? • Air pressure is equal in all directions. • So air pushes equally in all sides of us. The forces are balanced!

  9. We use barometers to measure air pressure. Mercury barometer: a glass tube sealed at the top partially filled with mercury. Air pressure pushing on the mercury in the dish causes the mercury to rise and fall in the tube. Measuring Air Pressure

  10. Aneroid Barometer: Works without liquid. Has an airtight metal can that is sensitive to changes in air pressure. This chamber is connected to a dial. Aneroid Barometers

  11. TV weather stations and aviation use inches of mercury. Meteorologists use millibars, an SI unit. A unit of pressure equal to one-thousandth of a bar or 100 pascals, most commonly used to measure atmospheric pressure. Units of Air Pressure

  12. Altitude (or elevation) is the distance above sea level. The higher ones altitude, the less air there is above you. So there will be less air pressure the higher one goes. Altitude and Pressure

  13. Pressure analogy • Imagine a stack of books. The bottom book feels all the weight of the all the books stacked above it, while the second one up feels slightly less weight. The higher in the stack, the less pressure one would feel.

  14. As the air pressure decreases, the density of the air decreases. The air particles are not squashed together as tightly the higher one goes. The air at sea level and at 6km has the same 21% oxygen, but at 6km there are fewer molecules, so you take in less oxygen with each breath. Altitude and Density

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