What you need:
- A spool
- A large rubber band
- A toothpick
- An unsharpened pencil
- Tape
- Scissors
- A metal washer (available at a hardware store)
What to do:
1. Thread the rubber band through the hollow centre of the spool. You should be able to see a bit of the band peeking out from both ends of the spool.
2. Break the toothpick so that it is just smaller than the diameter of the spool.
3. Push the toothpick through the rubber band at one end. Pull out and tighten the other end of the rubber band so that the toothpick is held tight against the spool.
4. Cut a small piece of tape and stick it over the toothpick to hold it in place.
5. On the other end of the spool, thread the rubber band through the washer. Push the washer in so that it rests against the spool.
6. Insert a quarter of the pencil through the loop of the rubber band. Wind up the band tightly using the pencil.
7. Set the spool down on its side on a table or on the floor and release the pencil.
What happens:
The spool whirls off like a wheel, pencil and all!
Why?
When you twirl the rubber band with the pencil, you are winding it up to store potential energy. The more you wind the band, the more energy it stores. Potential energy is the energy an object holds that can be used to do some work in the future. Simply put, it has the potential to do work based on its position, or its internal stresses or its electrical charge, etc.
It is the law of the world that energy cannot be created or destroyed; it can only change form. When you place the spool on the table and release the pencil, it starts to unwind. The potential energy of the band converts to kinetic energy. Kinetic energy is the energy that a body has due to motion. That’s what gets the spool rolling.
Picture Credit : Google
