A spring scale measures weight or force when an object is hung from its hook. It works in accordance with Hookes Law, which states that the force needed to extend or compress a spring by some distance scales linearly with respect to that distance. Therefore, the scale markings on the spring balance are equally spaced. The weight of an object is the force exerted on it by gravity, so a spring scale can be used to measure the weight of an object. To measure loose material such as sand, it can be poured into a plastic bag and hung from the hook of the spring scale.