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

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.

Air pressure is measured with a barometer .

Air pressure is measured in millibars or “inches of mercury”

29.92” Hg = 1,013 mbAverage height of barometric column at sea level

Altitude affects air pressure

pressure = force area

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.

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_engag

ement.htm• http://science.howstuffworks.com/transport/flight/mo

dern/hot-air-balloon5.htm

• Click link below to play:• Bill Nye "Smells Like Air Pressure"