Air Pressure. What is mass? Mass is the amount of matter in an object. Matter refers to atoms and...
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Transcript of Air Pressure. What is mass? Mass is the amount of matter in an object. Matter refers to atoms and...
Air Pressure
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.
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
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.
What is meant by VOLUME?• In math and science Volume is usually defined as the amount of space that something takes up.
larger force = larger pressure
smaller force = smaller pressure
larger area = smaller pressure
smaller area = larger pressure
Pressure is force pushing on an area.
pressure = force area
What is 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.
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 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.
When amount of mass in a given volume decreases, the
density also decreases.
Altitude increases and amount of air molecules decrease.
Less air molecules per given area also mean atmosphere is less DENSE at higher altitudes.
altitude density
Areas of high pressure push towards areas of low pressure.
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.
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