An object's internal energy measures its capacity to do work. Its internal energy at any height equals its kinetic energy when, after being released, it makes contact with the ground. Any change in height changes this internal energy. Besides the height, the two factors affecting the energy change are the body's mass and the acceleration due to gravity. The internal energy is proportional to both. Each object, of course, has its own mass, but gravitational acceleration is a constant at 9.81 meters per second squared.
Subtract the object's final height from its initial height. If, for instance, it drops from 100 meters to 80 meters, then 100 - 80 = 20.
Multiply the difference in height by the object's mass. For instance, if the object has a mass of 30 kilograms, then 20 * 30 = 600.
Multiply this answer by 9.81, so 600 * 9.81 = 5,886. This is the object's change in internal energy, measured in joules.