# Energy

## Potential And Kinetic Energy

Every object has energy as a consequence of its position in space and/or its motion. For example, a baseball poised on a railing at the top of the observation deck on the Empire State Building has potential energy because of its ability to fall off the railing and come crashing down onto the street. The potential energy of the baseball—as well as that of any other object—is dependent on two factors, its mass and its height above the ground. The formula for potential energy is p.e. = m × g × h, where m stands for mass, h for height above the ground, and g for the gravitational constant (9.8 m per second per second).

Potential energy is actually a manifestation of the gravitational attraction of two bodies for each other. The baseball on top of the Empire State Building has potential energy because of the gravitational force that tends to bring the ball and Earth together. When the ball falls, both Earth and ball are actually moving toward each other. Since Earth is so many times more massive than the ball, however, we do not see its very minute motion.

When an object falls, at least part of its potential energy is converted to kinetic energy, the energy due to an object's motion. The amount of kinetic energy possessed by an object is a function of two variables, its mass and its velocity. The formula for kinetic energy is k.e. = 1/2m × v2, where m is the mass of the object and v is its velocity. This formula shows that an object can have a lot of kinetic energy for two reasons. It can either be very heavy or it can be moving very fast. For that reason, a fairly light baseball falling over a very great distance and traveling at a very great speed can do as much damage as a much more massive object falling at a slower speed.