There are many ways to explore elastic potential energy. My favourite method, especially for young children, is by playing with rubber bands. In principal, the hands-on activity that I’m going to share will enable us to investigate the relationship between the height reached by a cup and the amount of “stretch” in a rubber band.
How straight forward could it be? (I’m trying to avoid from using the word simple here. Here are the items you need to collect, and usually it’s pretty easy to gather from the kitchen and your bedroom (may be)!
What you need:
1. Paper cups – hint: if you would like to test how high it could jump based on weight, you may want to gather different sizes and types of cups.
2. Rubber bands
5. Craft items for decoration, in order for you to turn your jumping cup into jumping frog, or a blast off rocket.
Divide the mouth of the cup into 4 equal parts. Mark it with a pencil or a felt pen.
Cut about 0.5cm at the marked points. Young children might need help with the marking and the scissors.
Take 2 rubber bands and tie them together. At this point, there are couple of ways to hone young children’s skills. First, we could show a visual guide as above, so that children can copy from the pictures. Secondly, we can also demonstrate the steps to them. Practice may help!
Insert rubber band to all 4 small cuts at the cup’s edge.
Decorate or paint it. Let it dry.
It’s time to launch and have some fun. How? Place the cup with rubber bands on top of another cup, press it firmly and let it go! Watch how high it will jump. Try to make few other pairs using different sized cups. What will happen if you launch from a taller cup?
What is actually happening? The moment we “press” the cup with the tied rubber band, we’re giving elastic potential energy to the cup. When it is released, the potential energy is converted to kinetic energy which makes the rocket shoot up. The stretchier the rubber bands, the higher potential energy the rocket gets.
Extension for older children (or even us, adults):
• Can you make the rocket go higher? Explore with different type of rubber bands.
• What will happen if we put weight on top of the rocket? Observe what happens when a marble size of clay is placed on top of the rocket.
• Besides the amount of stretch, what other variables might affect the height to which the cup rocket rises? Have you been able to control these variables in your experiment? Explain why or why not.
More to Explore (science never stops!)
Use your launcher to investigate launches at angles other than straight up. Instead of manipulating the amount of stretch, hold that variable constant and manipulate the angle of launch. Measure both the heights and distances of the rocket.
• CAUTION: Be careful not to aim the rocket near any of your classmates.