Source: Ketron Mitchell-Wynne, PhD, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA This experiment demonstrates the work-energy principle. Energy is one of the most important concepts in science and is not simple to define. This experiment will deal with two different kinds of energy: gravitational potential energy and translational kinetic energy. Gravitational potential energy is defined as the energy an object possesses because of its placement in a gravitational field. Objects that are high above the ground are said to have large gravitational potential energy. An object that is in motion from one location to another has translational kinetic energy. The most crucial aspect of energy is that the sum of all types of energy is conserved. In other words, the total energy of a system before and after any event may be transferred to different kinds of energy, wholly or partly, but the total energy will be the same before and after the event. This lab will demonstrate this conservation. Energy can be defined as "the ability to do work," which relates mechanical energy with work. Flying projectiles that hit stationary objects do work on those stationary objects, such as a cannonball hitting a brick wall and breaking it apart or a hammer driving a nail in to a piece of wood. In all cases, there is a force exerted on a body, which subsequently undergoes displacement. An object in motion has the ability to do work, and thus it has energy. In this case, it is kinetic energy. In this experiment, gravity will be doing work on gliders. The transfer of the potential energy of gravity to translational kinetic energy will be demonstrated in this experiment by sliding a glider down air tracks at various angles (i.e., heights), starting from rest. The potential energy of an object is directly proportional to its height. The net work done on an object is equal to the change in its kinetic energy; here, the glider will start from rest and then gain kinetic energy. This change in kinetic energy will be equal to the work done by gravity and will vary depending upon the starting height of the glider. The work-energy principle will be verified by measuring the starting height and the final velocity of the glider.