The Kinetic Energy equation is a simple way to calculate the energy of an object in motion.
It states that kinetic energy (E) equals one-half times mass (m) times velocity squared (v).
This means kinetic energy can never be negative, which may seem like an obvious statement.
However, there are some assumptions being made about the system that need to be discussed before anything else.
The kinetic energy equation assumes that the mass is constant.
This means if a body gains or loses some of its mass, then its velocity will change and thus so would the calculated kinetic energy.
Put another way, an object with more weight has more inertia to overcome which gives it less momentum for any given speed due to gravity pulling on it from all sides.
Likewise, when this same object slows down in order to stop at rest; not enough work results because there is no friction acting on this moving system.
In contrast, objects that are lighter have greater initial speeds but do not need as much force applied against them by external forces such as gravity.
So while these two systems may seem incompatible with each other they actually can co-exist within one.