The term energy may be defined as the capacity for doing work. There are two forms of energy: potential energy and kinetic energy.
Potential energy is the stored energy possessed by a system, because of the relative positions of the components of that system. If work done raises an object to a certain height, energy will be stored in that object in the form of the gravitational force. This energy, waiting to be released is called potential energy. The amount of potential energy a system possesses is equal to the work done on the system previously.
Potential energy can be found in forms other than weights and height. Electrically charged components contain potential (electrical) energy because of their position within an electric field. An explosive substance has chemical potential energy that is released in the form of light, heat and kinetic energy, when detonated.
A weight of 50 pounds is raised 5 feet. Using the formula:
Potential Energy = Force x Distance
= 50 x 5
= 250 ft-lb's.
Note: That energy is expressed in the same units as those used for work and in all cases energy is the product of force x distance.
Kinetic energy is the energy possessed by an object, resulting from the motion of that object. The magnitude of that energy depends on both the mass and speed of the object. This is demonstrated by the simple equation:
Energy =½mv2 or w v2
where m = mass, v = velocity (in feet or metres per second), w = weight, g = gravity (32 ft/sec2 or 9.81m/sec2).
All forms of energy convert into other forms by appropriate processes. In this process of transformation, either form of energy can be lost or gained but the total energy must remain the same.
A weight of 50lbs dropped from a height of 5 ft has kinetic energy of
KE = 50 x 25
2 x 32
= 19.53 ft-lb's