What are mechanical springs?
In their simplest form, Springs such as coil spring, leaf spring, volute spring, mainspring etc are elastic devices that store mechanical potential energy. It could be defined as a device that changes its shape when an external force is applied and returns to its original shape when the force it’s removed. The energy absorbed is stored in spring and can be recovered of the spring returns to its original shape.
Springs are very common in engineering product design and can be found in almost any engineering product from consumer to heavy industrial. Disassemble anything that involves a mechanism chances are you will find some type of spring. Even any battery holders have springs to keep the batteries in place and increase the contact.