What you need:
- An empty tin can
- Paperclips
- A 9V battery (small and rectangular) to serve as weight, you can use something of similar shape and weight as well
- Tape
- A thick and long rubber band
- A screwdriver
- Scissors
What to do:
1. Using the screwdriver, punch two holes, one into the lid of the can and the other into the can’s base. Make sure both holes line up. Get an adult to help you do this safely.
2. Tape the battery to the centre of the rubber band so that it hangs like a bell.
3. Insert one end of the rubber band through the hole in the base. Then slip the paperclip to the end of the rubber band that’s hanging outside the hole to ensure that the entire band doesn’t go into the can.
4. Repeat this with the lid of the can. So the weighted rubber band is now stretched out along the inside of the can.
5. Place the can on its side on a table or any flat surface. Roll it.
What happens:
If all goes well, the can should roll right back towards you!
Why?
When you roll the can, it gains kinetic energy which is nothing but the energy that an object has due to its motion. The faster the can rolls, the more kinetic energy it has.
It is the law of the world that energy cannot be created or destroyed; it can only change form. As the can rolls, the rubber band inside twists (as long as the weight hangs and doesn’t flip) and stores energy. This stored energy is known as potential energy which means the energy that gives an object the potential to do work in the future.
So, the kinetic energy of the moving can is changed into the potential energy of the twisting band: some of the kinetic energy is also lost due to friction. When all of the kinetic energy has been exhausted or converted, the can stops rolling forward. Since the band is fixed at both ends and has a weight holding its centre down, it cannot unwind without making the can roll backwards to release the potential energy stored in it. That’s how the can accomplishes its moon-roll!
Picture Credit : Google
