All energy can be in one of two states: potential energy or kinetic energy.
Energy can be transferred from potential to kinetic and between objects.
Potential energy is stored energy--energy ready
to go. A lawn mower filled with gasoline, a car on top of a hill, and
students waiting to go home from school are all examples of potential
Gravitational potential energy is the energy
possessed by a body because of its elevation (height) relative to a
lower elevation, that is, the energy that could be obtained by letting
it fall to a lower elevation. For example, water at the top of a
waterfall or stored behind a dam at a hydroelectric plant has
gravitational potential energy.
Most of the energy under our control is in the form of potential
energy. Potential energy can be viewed as motion waiting to happen.
When the motion is needed, potential energy can be changed into one of
the six forms of kinetic energy.
Kinetic energy is energy at work. A lawn mower cutting grass, a
car racing down a hill, and students running home from school are
examples of kinetic energy. So is the light energy emitted by lamps.
Even electrical energy is kinetic energy. Whenever we use energy to do work, it is in the kinetic state.
The kinetic energy of an object is the energy which it possesses due to its motion.
In classical mechanics, the kinetic energy of a non-rotating object of mass m traveling at a speed v is ½ mv². In relativistic mechanics, this is only a good approximation when v is much less than the speed of light.
In physics, potential energy is the energy of a body or a system with respect to the position of the body or the arrangement of the particles of the system.
The SI unit of measure for energy and work is the Joule (symbol J).
g=acceleration due to gravity