The formula of conservation law of mechanical energy is e 1 equal to e2 or ek2 plus ep2 equal to ek 1 plus ep 1, where e 1 and e2 respectively represent the initial and final mechanical energy of the system, ek represents kinetic energy and ep represents potential energy. This law shows that the mechanical energy of the system remains unchanged when only gravity or elasticity does work in the system. The applicable conditions of the law of conservation of mechanical energy include: only gravity or elasticity does work in the system, the work done by other forces is zero, and there is no transmission of mechanical energy between the system and the outside world, that is, the system is a closed system, and there is no inflow or outflow of mechanical energy, and the mechanical energy is not converted into other forms of energy, such as internal energy and electric energy.