A flexible elastic object to store mechanical energy. It has a unique name and the following parameters:

- rest length: is the length of the spring as it is not compressed or stretched.
- length: is the initial spring length
- stiffness: is the level of spring resistance to compression or stretching
- damping: is level of spring ability to disperse stored energy, an internal viscosity
- body 1 and 2: are the bodies to which the spring is fixed
- local position 1 and 2: are the local positions of the spring ends relative to its centre in the non-deformed state
- position 1 and 2: are the global positions of the spring ends
- force: is the force that acts along the spring