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Elasticity

المؤلف:  GEORGE A. HOADLEY

المصدر:  Essentials of Physics

الجزء والصفحة:  p-17

2025-10-20

490

When a tennis ball is compressed into smaller volume between the hands, it feels springy, or elastic, because the contained air tends to resume its original volume; that is, the molecules tend to regain their original distance apart. All gases and liquids, and to a certain ex-tent solids also, show a similar reaction against external pressure, and are said to have elasticity of volume. When the shape of a solid body is slightly changed by an external force, it usually tends to resume its original form. This elasticity of form may be classified as follows (the corresponding external forces being given in parentheses) :

1. Elasticity of Compression (pressure); it is shown, for example, by the rebound of a solid rubber ball dropped upon the floor, or by the recoil of a compressed spring.
2. Elasticity of Traction (pulling); it is illustrated by a rubber band stretched around a book and holding it shut.
3. Elasticity of Flexion (bending); it is shown by the vibration of a tuning fork, or of a steel wire one end of which is clamped in a vise.
4. Elasticity of Torsion (twisting); an example is the untwisting of a rubber tube when it is held at one end and the other let go after being twisted.