The force of elasticity
If we stretch, squeeze or bend a body, its shape changes (deformation). If after release it returns to its original shape, the body is elastic and the restoring force is the elastic force. A spring, rubber, a ball and a bow are elastic. Plasticine and clay keep their new shape — they are not elastic. The more we stretch a spring, the larger its pull. This property is used in a spring balance (dynamometer): the spring stretches under a load and the scale shows the force. Elastic force is useful in mattresses, shock absorbers, watch springs and trampolines. A spring or rubber stretched too far may not return or may break. Do not pull rubber close to your face and let go; you could get hurt.
Hang different loads (for example 1, 2, 3 pencils) on a rubber band or spring and measure its stretched length with a ruler. Does stretch grow with load?