Grades K–2 · Materials & Matter
Why does a stretched rubber band pull back?
A rubber band changes shape when something pulls its ends apart. At the same time, the band pulls back on the things stretching it. That pull can be felt before the band is released.
In the diagramRubber’s network changes arrangementRelaxedStretchedChains are enlarged; real rubber has many crosslinksStretching stores energy; recovery has limits.
Inside rubber are very long, tiny chains of connected atoms. In relaxed rubber, the chains have many bends. Stretching changes their arrangement, making many parts line up more along the pull.
When the pull is removed, the network of chains can return toward its relaxed arrangement. Some energy stored during stretching can become movement again. A band stretched too far may be damaged and may not return to its old shape.
About this explanation
Starting knowledge: Compare a relaxed shape with a stretched shape and recognize a pulling force.
Sources
- OpenStax — Organic Chemistry: Diene Polymers, Natural and Synthetic Rubbers