Answer:
Rubber is made from long-chain molecules, called polymers, which are normally all scrunched up. When you stretch a rubber band, you straighten the molecules and pull them apart, so the rubber gets longer. When you let go, cross-link bonds between the polymers help to snap them back into place. This is what makes an elastic material such as rubber (one that returns to its original shape and size) different from a plastic material (one that changes shape but doesn't go back exactly to how it was), which includes most metals as well as most plastics.
Explanation:
Rubber is made of polymers. When the elastic band is at rest, the molecules are entangled with each other and do not have a particular direction, but when the elastic is stretched, they all align. The molecules of the polymer are not stretched, they are aligned in a different way. Therefore, there is no difference in energy, but there is a difference in entropy. When the elastic band is released, all the polymers are randomly agitated by thermal movement, and lose their alignment, so they return to the tangled state, causing the elastic to contract. This is known as entropic force.
