Bouncy balls are awesome. If you drop them, they come most of the way back. If you throw them down really hard, they can bounce all the way up to the ceiling. They can do this because of the fact that energy is conserved. That means the amount of energy in a system will stay the same — it just might come in different forms. This activity is going to involve bouncy balls and shooting straws to demonstrate different types of energy.
Student Guide
Straw Rockets
Experimenting with gravity
How does the bounce height of a ball change with the height from which it’s dropped?
This resource was originally published in PhysicsQuest 2018: Force.
How does the bounce height of a ball change with the height from which it’s dropped?
- Bouncy Ball
- Straw
- Wire
- Meter stick
- Scissors
- Large sheet of paper
- Pen or pencil
- Tape
Intro
Before the experiment
- What would bounce higher, a ball dropped from 10 feet or a ball dropped from 100 ft? Why?
Setting up
Jam the wire in the bouncy ball so that it’s sticking straight up.
Place the straw over the wire (like a sleeve) and cut the straw so it is a bit shorter than the wire sticking out of the ball.
There should be enough of the wire above the straw that you can hold onto the wire without touching the straw.
Tape a giant piece of paper to the bottom of the wall.
During the experiment
Collecting data
Qualitative
Place the straw over the wire. Then hold the bouncy ball by the tip of the wire, without touching the straw, a few feet above the ground.
Drop the ball, making sure that it hits the ground with the straw at the top and as perpendicular to the floor as possible. Don’t slam the ball down - just let it drop out of your hand. Make sure the floor is hard (wood, tile, stone, etc.), not carpeted.
- What happened?
Now drop the ball in the same way, only from a lower height.
- What happened?
Drop the ball from a higher height than you did initially.
How do the height of the drop and the height of the rebounding rocket compare?
Quantitative
Hold a meter stick next to the piece of paper taped on the wall. Make sure the floor is hard (wood, tile, stone, etc.), not carpeted.
Hold the ball/straw combo just as you did in the qualitative experiment. Start with the combo 15 cm above the floor.
Drop the ball and have another team member make a mark at the highest point of the straw’s trajectory as it flies upward.
Repeat five more times and average the five trials. Be aware that some of your tests might not work, but that’s okay.
Increase the height to 20 cm and repeat steps 1-4.
Continue in 5 cm increments until you can no longer reach the top of the straw’s trajectory to measure it.
Analyzing data
Qualitatively, how did the height of the straw’s flight compare to the height at which it started?
What type of energy do the ball and straw have right before they drop?
- What about when they hit the ground?
- When do they rebound?
- At the top of the straw’s trajectory?
On the next page, graph the height the straw reached (in cm) versus the height from which it was dropped (in cm).
- What does the graph look like?
- How high do you think the straw might go if the ball was dropped from 5 m?
Why do you think the straw could go as high as it did?
Conclusion
- Draw a diagram of the experiment and label what forces are present.