① control mechanical movement, such as valve spring in internal combustion engine, control spring in clutch, etc.
② absorb vibration and impact energy, such as the buffer spring under the car and train carriage, the vibration absorption spring in the coupling, etc.
③ store and output energy as power, such as clock spring, gun spring, etc.
④ used as a force measuring element, such as the spring in the force measuring device and spring scale. The ratio of the load to the deformation of the spring is called the spring stiffness. The greater the stiffness is, the harder the spring will be.