Then, dividing the units of energy (such as eV) by a fundamental constant that has units of velocity (L T −1), facilitates the required conversion of using energy units to describe momentum. In the field of high-energy particle physics, the fundamental velocity unit is the speed of light in vacuum c.
https://en.wikipedia.org/wiki/Electronvolt
Joule is the unit of energy used by the International Standard of Units (SI). It is defined as the amount of work done on a body by a one Newton force that moves the body over a distance of one meter.
http://www.universetoday.com/61490/what-is-a-joule/
Like the elementary charge on which it is based, it is not an independent quantity but is equal to 1 J/C √2hα / μ0c0. It is a common unit of energy within physics, widely used in solid state, atomic, nuclear, and particle physics.
https://en.wikipedia.org/wiki/Electronvolt
Conversely, work done on a body changes the energy of the body. Let’s go back to the apple example mentioned earlier to elaborate. An apple is a favorite example to illustrate a one joule of work when using the definition given earlier (i.e., the amount of work done ….) because an apple weighs approximately one Newton.
http://www.universetoday.com/61490/what-is-a-joule/
The joule is a unit of measure for energy. Sitting quietly, a person generates 100 J of heat every second. Individuals pay per kilowatt hour for the electricity they use in their homes. The amount of energy required to lift an apple 1 meter (3.3 feet) is roughly equivalent to 1 Joule.
http://www.wisegeek.org/what-is-a-joule.htm
Examples. To get an idea of how much energy a joule actually is, it helps to look at some everyday examples. A joule is the amount of energy needed to raise the temperature of 1 gram of cool, dry air by 1.8°F (1.0°C). An average person sitting quietly produces 100 J of heat every second. The amount of energy required to lift a small apple 1 meter (3.3 feet) against the Earth's gravity is roughly equivalent to 1 J.
http://www.wisegeek.org/what-is-a-joule.htm
In physics, the electronvolt (symbol eV; also written electron volt) is a unit of energy equal to approximately 160 zeptojoules (symbol zJ) or 6981160000000000000♠1.6×10−19 joules (symbol J).
https://en.wikipedia.org/wiki/Electronvolt
In high-energy physics, the electron volt is often used as a unit of momentum. A potential difference of 1 volt causes an electron to gain an amount of energy (i.e., 6981160217648700000♠1 eV).
https://en.wikipedia.org/wiki/Electronvolt
In particle physics, a system of natural units in which the speed of light in vacuum c and the reduced Planck constant ħ are dimensionless and equal to unity is widely used: c = ħ = 1.
https://en.wikipedia.org/wiki/Electronvolt
At the top, the apple would have gained about one joule of potential energy. Also, when the apple is one meter above its original position, say the floor, gravity would have gained the ability to do work on it. This ability, when measured in joules, is equivalent to one joule. Meaning, when you release the apple, the force of gravity, which is simply just the weight of the body and equivalent to one Newton, would be able to perform one joule of work on it when the apple drops down from a height of one meter. Mathematically, 1 joule = 1 Newton ⋅ meter.
http://www.universetoday.com/61490/what-is-a-joule/
a joule is equal to what
A joule is equal to 1 Newton. A joule is equal to 1 Newton meeter.