Springs, gravity, and other forms of stored energy, used with leverage can provide a simple and effective means for actuating devices. For example, cranking the handle of a music box compresses a spring which drives the device. A spring can be any material that is designed to resist a change in shape. The spring constant defines how much force must be generated in order to stretch, compress, bend or deflect a spring a certain amount. There are several types of springs, each of which is best suited to oppose a change in shape in a particular direction.
Compression springs are the most common.
Compression springs can be found in a wide range of sizes and strengths, from tiny, light duty springs found in a lock barrel, to large, heavy-duty shock absorber springs on an automobile. The spring constant of compression springs defines how much the length decreases under a certain load. Torsion springs are designed to resist twisting. Torque is rotational force and degrees or radians are rotational distance. Torsion springs are used to move or support rotating objects such as hinges or levers.