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The Properties of Air

Lesson 1

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The Properties of Air

Air takes up space, and has mass

Air is affected by heat

Air exerts pressure

Air can be compressed

Air is affected by altitude

We are going to focus on�2 properties during this lesson:

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AIR EXERTS�PRESSURE

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Air exerts pressure/pushes on an object

  • On a windy day, you can feel the pressure of air against your face
    • Wind is simply moving air

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Air exerts pressure/pushes on an object

  • Even when air is not moving, it exerts pressure
  • Air presses hard against all sides of everything it touches
  • It never stops pressing!

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Air exerts pressure/pushes on an object

  • Air does not exert the same amount of pressure everywhere
  • Air has a mass and exerts pressure downward due to gravity’s force
    • so the higher you go the less air there is above, therefore the lower the air pressure.

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Air exerts pressure/pushes on an object

  • Air does not exert the same amount of pressure everywhere
  • Air has a mass and exerts pressure downward due to gravity’s force
    • so the higher you go the less air there is above, therefore the lower the air pressure.

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Air exerts pressure/pushes on an object

  • You have probably felt a change in air pressure if you have ever been in a fast-moving elevator going up a tall building
  • The pressure of the air inside the elevator decreases the higher you climb
    • but the air pressure inside your body remains the same.
    • This means the air pressure inside your body is higher than the air pressure in the elevator as you ascend

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Air exerts pressure/pushes on an object

  • This imbalance in pressure makes your eardrums bulge out slightly until some air forces its way out of your ears and you feel them “pop”

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  • This happens because air tends to flow from areas of higher pressure to areas of lower pressure

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AIR TAKES UP SPACE AND HAS A MASS

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Air takes up space and has a mass

  • Sometimes people use the terms mass and weight to mean the same thing, but they have different meanings.
    • What is the difference?

MASS is the amount of matter in an object or substance

WEIGHT is the force of gravity pulling on a mass

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MASS VS. WEIGHT

your MASS is the same whether you are one the Earth or the Moon but your WEIGHT changes

The Moon exerts about �1.6 N per kg of mass

The Earth exerts about �9.8 N per kg of mass

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Air takes up space and has a mass

  • An object’s mass rarely changes
  • An object’s weight does change…
    • depending on how strong the force of gravity is

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  • The stronger the force of gravity
    • the greater an object’s weight
  • the weaker the force of gravity
    • the lower an object’s weight.

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Air takes up space and has a mass

  • On the moon, the force of gravity is 6 times less than that on Earth.
  • Therefore, your weight on the moon is 1/6th of your weight on Earth

HOW MUCH DO YOU “WEIGH” ON THE MOON?

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Air takes up space and has a mass

  • Mass and weight are directly proportional;
    • the greater an object’s mass the greater its weight

MASS

How heavy something is

WEIGHT

How heavy something is + How heavy gravity is

(mass) + (gravity)

Even though air is invisible… air has mass

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Air takes up space and has a mass

  • Air is made of gases (that each have mass):
    • nitrogen
    • oxygen
    • water vapor
    • other materials

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  • These substances are what give air mass.

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