Spring, in mechanics, a device that can absorb and release energy by a change in its shape. Springs can be made in a wide variety of types and sizes from almost any material that has elasticity (the ability to regain its shape and size after being deformed). Steel and other metals are the most frequently used spring materials. A familiar use for springs is as a cushion between the wheels and body of a motor vehicle or railway car. Other uses include the absorbing of vibrations, providing motive power in watches and other wind-up mechanisms, and furnishing power for devices such as door closers.

Several types of springs in common use can be classified by shape. The coil, or helical, spring is a metal wire or rod wound into a cylindrical shape. It can be designed either to compress under a force or to resist force as it is stretched. Flat, or leaf, springs consist of one or more relatively long metal strips; they are commonly used in suspension systems of motor vehicles. The spiral spring, used to drive wind-up mechanisms, twists outward from its center. Other types of springs include the disk spring, which is usually a curved or tapered washer; and the torsion bar.