1. Air Pressure

2. What is mass? Mass is the amount of matter in an object.
Matter refers to atoms and molecules
Even if gravity changes, mass stays the same
Mass is not the same as weight. Weight depends on gravity. Weight is measured in pounds or kilograms, ounces or grams.

3. What is gravity?
A force of attraction between any objects that have mass
On Earth, the center of gravity is Earth’s inner core.
Earth’s gravity keeps the atmosphere from floating away, makes things fall, and prevents us from jumping too high
Anything with mass has a gravitational pull.
More massive = more gravitational pull

4. What is Density?
Density is a way of describing how tightly packed a substance is, or how close together its molecules and atoms are, or how much mass is in a given volume
More mass in a given volume
= more dense
Less mass in a given volume
= less dense
Dense things cram a lot of mass into a small space.

5. What is meant by VOLUME?
In math and science Volume is usually defined as the amount of space that something takes up.

6. Pressure is force pushing on an area. pressure = force area
What is 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

7. 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.

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

9. 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

10. Altitude affects air pressure
pressure = force
area
Increasing altitude means less and less air molecules per given area. Less molecules in a given area means lower density. Less molecules also 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.
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

11. 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.
When amount of mass in a given volume decreases, the density also decreases.
altitude
density

12. Areas of high pressure push towards areas of low pressure.

13. 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.

14. 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.

15. Click the links below for more fun!
Basketball and Air Pressure Interactive
NOVA Floating and Sinking Interactive
Air Pressure Video Clip
Eureka! Volume and Density
Eureka! Buoyancy