Rubber is made up of polymer molecules. That is, the molecules join one another and form a long chain. The chains are rolled up in normal condition. Then they are compressed. When the two ends of the rubber are pulled, the molecules are in a state of straight tension along the two sides, like a hard rope. After this condition, if the rubber is pulled, it will not be longer , but if it is released, it will return to its previous condition. When the elastic force is released between the chains, the chain of granules returns as before. Again, as before, the random contraction takes place. Many polymer products are hard. This is because even though they have a large number of atoms in their molecules, they do not stand like a twisted rope. As a result, even if they are pulled, they do not get long. [Elastic force: The force that moves the object to its previous position at the end of work. For example , when the spring is pulled, it shrinks as before. Eraser pressure to wipe pencil stains is small. When the pressure is removed, it returns to its previous shape]