Air Pressure

Pressure is force pushing on an area. pressure = force area larger force = larger pressure smaller force = smaller pressure larger area = smaller pressure smaller area = larger pressure Same force + larger area = more spread our force, so pressure is less….same force + smaller area localizes the force, so pressure is greater

Air Pressure = molecules pushing (exerting force) on other molecules At sea level a 300-mile high column of air molecules push down with a force of 14.7 pounds per square inch (psi), or 1 kg per square centimeter (kg/cm2). That’s like having an elephant sitting on your head.

We aren't pushed around or squashed by this pressure because the forces on all sides of us balance one another out.

Try this: Lay a ruler on a table with about 3” hanging over the edge. Lay a sheet of printer paper on the part of the ruler in direct contact with the table. Press down on part of the ruler hanging over the edge. Observe. Repeat with an opened sheet of newspaper. Observe and explain any differences. The student will discover the newspaper was much harder to lift than the printer paper. As the ruler lifted the printer paper, air rush in under the rising paper and thereby quickly allowed the air pressure to equalize on all sides. Essentially, the weight of the air above the paper had no effect on the difficulty in lifting the paper. As the ruler lifted the newspaper, the edges of the newspaper remained in contact with the desk. Very little air was allowed to rush in and equalize the pressure on the bottom side of the newspaper. Since there is less air below the paper the pressure is less as well. Now the weight of all the air above the paper now becomes more evident

Air pressure is measured with a barometer . A falling" barometer means that low-pressure mass of air is approaching. Such low-pressure systems generally bring storms. A rising" barometer generally means an approaching high-pressure air mass and fairer weather Air pressure is measured in millibars or “inches of mercury” 29.92” Hg = 1,013 mb Average height of barometric column at sea level

Altitude affects air pressure pressure = force area Gravity pulls all things down, so the most air molecules are closest to Earth’s surface, at sea level …actually there are even more at Death Valley in CA because it’s below sea level Increasing altitude means less and less air molecules per given area. Less molecules means less pressure (force exerted) because fewer molecules collide. Also, it’s colder up there which causes molecules to slow down and collide with less force.

Altitude increases and amount of air molecules decrease Altitude increases and amount of air molecules decrease. Less air molecules per given area also mean atmosphere is less DENSE at higher altitudes. D = M V When amount of mass in a given volume decreases, the density also decreases. altitude density

Temperature affects pressure Heating causes molecules to move faster. Moving faster increases the amount of collisions between individual molecules and the relative force of those collisions. More force results in more pressure. Faster moving molecules exert greater pressure on a rigid container. If there is no container, then faster molecules will move apart.

What happened? Burning candle consumes oxygen from air inside glass. This reduces mass & density of air in glass and therefore, the air pressure. Candle goes out, heat source is gone causing gas molecules to slow down  further drop in air pressure. Outside pressure is now greater than inside. Difference in air pressure pushes water from pan (outside) up into the glass. High pressure area pushes towards low pressure area.

Areas of high pressure push towards areas of low pressure.

Works Cited http://dogfoose.com/wp-content/uploads/2011/04/Dogfoose-header3.jpg http://www.vias.org/kas/en/air_pressure.html http://www.srh.noaa.gov/srh/jetstream/atmos/ll_engagement.htm http://science.howstuffworks.com/transport/flight/modern/hot-air-balloon5.htm Click link below to play: Bill Nye "Smells Like Air Pressure"