1. Gases

2. Gases are defined as having no definite volume and no definite shape.
Some properties of gases are
They expand to fill their containers.
They have very low densities
They can flow/ diffuse
They exert a pressure

3. What is pressure? Pressure is defined as the force exerted over an area
What are some things that have air pressure?
Car tires
Beach balls
Inflatable jumpers
Helium balloons

5. What is pressure? Pressure is defined as the force exerted over an area
If size stays the same, the pressure outside is equal to the pressure inside. (yellow)
If the size decreases, the pressure outside is greater than the pressure inside. (blue)
If the size increases, the pressure outside is less than the pressure inside.
What are some things that have air pressure?
Car tires
Beach balls
Inflatable jumpers
Helium balloons
Hot air balloons

6. Before the balloon is blown up
Let’s try to draw those pressures…
Before the balloon is blown up
all the outside air is pushing on the balloon.
(no inside air to push back = flat as a pancake)

7. But, after the balloon is blown up
air outside is pushing “in”
AND, air inside is pushing “out”
Since the balloon stays the same size, the pressure (pushing) inside the balloon MUST be the same as the pressure outside the balloon.

8. What about after the vacuum pump?
Air inside is pushing more (has greater air pressure)
than the air outside so it allows the balloon to expand!

9. What two variables are changing?
Since the pressure outside decreased, the volume (size) of the balloon increased.