Have you ever seen a hot air balloon floating in the sky? What keeps them up? Why do they have to be so big? Why don't they usually fly in the middle of the day?
If you've ever wondered about these questions, or if you just think "air is a gas," then have I got challenge for you!
What you'll need to play along:
Begin by filling up your ball to its standard pressure. Have a friend hold the meter stick so that it's sticking straight up from the floor. Drop (DON'T THROW) the ball onto the floor from about waist height next to the meter stick. Measure how high up it bounces. Make sure and measure from the bottom of the ball and repeat 2 or 3 times so that you get about the same amount each time. This measurement will be your "control bounce."
Okay, so here's the challenge:
What will happen to the bounciness of a ball if you cool it down or heat it up?
What you do:Begin by predicting what will happen as you either heat or cool the ball. Will a warmer ball bounce higher than a cooler ball? After you make your prediction, place the ball in a refrigerator or cooler with ice for about 15 minutes. Take it out and try bouncing it again. Remember to drop it from the exact same height on the exact same floor and measure the exact same way! How does this number compare to your "control bounce"?
Let the ball heat up to room temperature again and then use the hair dryer to heat it up for about 2-3 minutes. Test it again. Was your prediction right? What in the world does this have to do with a hot air balloon?
Curriculum Focus: Science/Physics/Air and temperature
An introduction to the scientific principles involved in hot air ballooning. This site is primarily for teachers in the elementary grades.