1. AIR PRESSURE

2. What is pressure? A force that is applied over an area.

3. What is air pressure? Balloon example – what about the particles is causing pressure in the balloon? Air pressure is caused by the particles of air colliding with sides of the container (in this case, the balloon)

4. What is atmospheric pressure? What is the Earth’s atmosphere made up of? Why does Earth have an atmosphere?

5. Gravity and Atmospheric Pressure The stronger the gravity, the more gas is held by the world and the greater the weight of atmospheric pressure on a point.

6. Atmospheric Pressure Atmospheric pressure – the amount of force (gravity) exerted on 1 meter 2 column of air.

7. High altitudes = lower pressure Low altitudes = higher pressure

8. What would be the units of pressure? Pressure is a force that is exerted on an area. Units of Pressure: – Atmosphere (atm.) – pounds per square inch or psi (1 atm. = 14.7 pounds per square inch) – mm or inches of mercury (1 atm.= 760 mm or 29.92 inches of Hg) – torrs (1 torr = the pressure exerted by 1 cm of mercury) – Pascal or Pa(1 newton per square meter) 1 kPa = 1000 Pa and 1 atm. = 101.325 kPa

9. http://www.youtube.com/watch?v=HUmZrtiXDik

10. What happens when you draw a liquid through a straw into your mouth? When you suck on a straw, you remove some of the particles of air in the straw. Since there are more particles of air striking the liquid in the cup than are striking the liquid in the straw, the effect of these extra collisions is to push the liquid up into your mouth. So actually, you are not sucking the liquid into your mouth, the atmosphere is pushing it there.

11. Evangelista Torricelli (1606-1647) Torricelli wanted to figure out why he could not pump liquid up to the top floor of his villa with a pump. He reasoned that even if the pump could remove all the air above the column of liquid, the pressure exerted by the atmosphere could only support a column of liquid so high (~34 ft). As the story goes, he replaced the top portion of the pipe with a glass tube and noted that the water level fluctuated depending on the weather. He found that he could more conveniently study this behavior if he used a liquid with a greater density. He filled the tube with mercury (d = 13.6 g/mL) and found that atmosphere could pressure could support a column of mercury varying from 28-31 inches. Such a device is called a barometer.

12. Torricelli’s barometer used a glass column suspended in a bowl of mercury. The pressure of the air molecules pushed the mercury up into the glass tube. The weight of the mercury in the tube was equal to the weight of the air pressing down on the mercury in the dish.

13. As atmospheric pressure increases… The mercury in the tube rises.

14. Another Instrument used to measure pressure… Manometer

15. Manometers Cont.