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Name: Samantha T.
Status: student
Age:   13
Location: N/A
Country: N/A
Date: 1999-2001


Question:
Why does a rubber band stretch?


Replies:
Hi, Samantha !!

Think of rubber as thousands of long molecules, like chains. These long molecules are called "polymers". They are bound together in a crisscross fashion, like a net of molecules. If by means of a force they are stretched, they uncoil and straighten. If the force ceases, the chains relax and bunch up again. When stretched, the long chains gather energy (potential, like gather coils of an old clock). Free from the stretching force, the potential energy makes the molecules return to its initial state, and this is called "elasticity".

Alcir Grohmann
Beschaffung SAM


Rubber is composed of long hydrocarbon chains that are interlinked to one another at very distant intervals along the polymer backbone. These chains tend to form random coils -- you might think of them as very long chains of spaghetti. When you pull on the rubber band, the chains tend to uncoil and partially align with one another. However, because the chains are linked together by these bridging bonds, there is a limit to how much the coils can be stretched out. When that point is reached it gets harder to stretch the rubber band any further.

When you let go of the stretched rubber band the extended coils re-coil because there is no longer a force tending to align them -- the rubber band snaps back to its original limp condition.

The complete quantitative treatment of rubber elasticity is fairly advanced for even high school level chemistry, but it does exist.

Vince Calder



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