# Talk:energy

Encyclopaedic info cut from definition: " Matter technically would not exist without energy because it is composed of energy as was shown in the equation *E = m C²*." Paul G 11:58, 18 Dec 2003 (UTC)

- Equation is wrong - 'C' should be lower case; no space needed between m and c. Paul G 11:58, 18 Dec 2003 (UTC)

Kinetic energy

The standard textbook definition of energy is the "ability to do work." Unfortunately, this definition does not really give a good picture of what energy is all about. We normally think of an object having energy as one that is moving. The energy of a moving object is called kinetic energy and is abbreviated as KE.

The properties of kinetic energy are that the greater the mass of a moving object, the greater its energy will be. Also, the faster it goes, the greater its energy. That energy is proportional to the square of the velocity.

The equation for calculating the kinetic energy of an object is

KE = ½ mv²

where:

* m is the mass of the object * v is its speed of velocity and v² is the velocity squared or v times v * ½ mv² is one-half times m times v²

Note that the velocity of the object must be much less than the speed of light. When the speed of an object—such as an atomic particle—approaches the speed of light (c), its kinetic energy approaches E = mc², according to the Theory of Relativity. Potential Energy

There are situations when an object has the potential to start moving and gain kinetic energy. Often there are forces acting on the object, but the forces aren't yet sufficient to move the object. Potential due to gravity

If you hold an object a distance from the floor, it has the potential to start moving, once you let it go. The force of gravity is pulling on the object, giving it potential energy. The equation is

PE = mgh

where:

* PE is the potential energy * m is its mass * g is the acceleration of gravity (32 ft/s² or 9.8 m/s²) * mg is the weight of the object (m times g) * h is the height of the object from the floor or ground

PE becomes KE

If you drop the object, its potential energy will become the kinetic energy of motion (PE = KE).

Since PE = mgh and KE = ½ mv², then:

mgh = ½ mv²

You can determine the speed it will be traveling after falling a height h by solving the equation for v:

v² = 2gh

Take the square root of both sides of the equation:

v = SQRT(2gh) or v = √(2gh)

Note that the mass m cancels out of the equation, meaning that all objects fall at the same rate.

Thus, if h = 1 ft, and since g = 32 ft/s², then v² = 2*32*1 = 64 and v = √64 = 8 ft/s. Other types of PE

Other examples of potential energy that could cause motion include explosive chemical compounds and a coiled spring, ready to be released. A stretched rubber band, also has potential energy.

With chemical explosives, it is difficult to calculate the potential energy without experimenting to see how much kinetic energy is released in an explosion.

With a compressed spring, there are calculations that can determine its strength and potential energy.