Kinetic and potential energy are both typically ascribed as forms of mechanical energy and can be interchangeably converted. Potential energy can be converted into kinetic energy and vice versa, but the change is always accompanied by the dissipation of some energy as heat.
Kinetic energy is the energy of a body due to movement, while potential energy is the energy of a body by virtue of its position or state. The kinetic energy of a body depends on its frame of reference. A body matching velocity with its reference frame is stationary in that reference frame but moving in another reference frame. In the frame where the body appears stationary, its kinetic energy is zero. Kinetic energy is proportional to square the velocity and the mass according to the Newtonian laws of motion and must be assigned real, positive values, as neither real mass nor velocity squared can be negative. As the velocity increases at one rate, the kinetic energy increases at square this rate.
Potential energy also depends on the reference frame. Gravitational potential energy is directly proportional to height. Depending on the reference level from which the height is measured, potential energy can be positive, negative or zero.