Energy cannot be created or destroyed; it can only be transformed from one form to another or transferred from one body to another.
One specific case of the law of conservation of energy is the law of conservation of mechanical energy:
In a system without friction, the mechanical energy of a body remains constant.
According to the law of conservation of mechanical energy, in an isolated system where only conservative forces act between bodies, the total mechanical energy of the system is constant. For example, in the case of free fall under the influence of Earth's gravity, potential energy is converted into kinetic energy, but their sum remains constant.
If there is no frictional force acting on the body, the following formula applies:
$$E_{k1}+E_{p1}=E_{k2}+E_{p2}$$
where,
Ek1, Ek2— kinetic energy;
Ep1, Ep2— potential energy.