1. DENSITY
PRESSURE
and

2. Which is heavier…
A basketball?
Or a bowling ball?

3. Or a styrofoam block of the same size?
Which is heavier…
A metal block?
Or a styrofoam block of the same size?

4. Size Doesn’t Matter!
Objects that are the same size could have very different masses!
All materials are made of small particles called molecules…

5. They may be closely packed, like in a heavy metal block…
DENSITY
The molecules in different objects are arranged differently.
They may be closely packed, like in a heavy metal block…

6. Or they could be spaced out, like in a styrofoam block.
DENSITY
The molecules in different objects are arranged differently.
Or they could be spaced out, like in a styrofoam block.

7. DENSITY LOW density HIGH density
DENSITY describes how closely packed the particles of an object are.
HIGH density
LOW density

8. How does this relate to air?
We know that air has mass…
Air molecules are spread very far apart compared to molecules in a solid, like metal.
Which means that air is also made of molecules.

9. How does this relate to air?
Even though air molecules are spread far apart, the air in our atmosphere stretches up over 60 miles!
The air above your head actually weighs about as much as a school bus!
It doesn’t crush you, though, because it is pushing on all sides.

10. How does this relate to air?
This pushing of air is called AIR PRESSURE.
You felt PRESSURE when you were crammed into the tape square.
…………………………………………………………………………………………………………………………………………
Air at LOW DENSITY also has LOW PRESSURE
Air at HIGH DENSITY also has HIGH PRESSURE