Kinetic energy is the energy that a body contains due to being in motion. Kinetic energy is the amount of work required to accelerate a body of a given mass to a certain speed (linear or rotational). This energy obtained during acceleration will remain unchanged as long as this body does not vary its speed.

In classical mechanics, the linear kinetic energy (without rotation) of an object of mass m traveling at a speed v is ½ · m · v ^{2} . In relativistic mechanics this is a good approximation only when the speed is much lower than the speed of light.

The unit of measurement for kinetic energy in the international system of units is July (J).

## Energy transformation

Energy can manifest in many forms, including chemical energy, thermal energy, electromagnetic radiation, gravitational energy, electrical energy, elastic energy, nuclear energy, and energy from the rest. All of these types of energy can be classified into two main classes: potential energy and kinetic energy. Kinetic energy is the energy of movement of an object. Kinetic energy can be transferred between objects and transformed into other types of energy.

### Examples of transformation of kinetic energy

Energy of one type can be transformed into energy of another type. An example will be useful to understand this aspect. A motorcyclist uses the chemical energy provided by the combustion of gasoline in a thermal engine to accelerate the motorcycle to a certain speed. On a level surface, this speed can be maintained without further work, except to overcome air resistance and friction with air and between engine elements. Chemical energy has been converted to kinetic energy, the energy of motion, but the process is not completely efficient and produces heat within the engine.

At some point, the rider could take advantage of this speed to climb a hill until the bike was stopped a few meters higher. At this time, all the kinetic energy has been converted to potential energy. If the rider wishes, he can take advantage of the descent to recover speed, at this moment the potential energy will be converted into kinetic energy again.

Because kinetic energy depends on speed, this type of energy depends on the frame of reference of the observer. The speed of the motorcycle is not the same from the point of view of the biker (in this case it would be zero), that of an observer who observes it on the side of the road or that of an astronaut who observes it from a car in the opposite direction .

Kinetic energy can pass from one object to another. This effect can be seen the moment a billiard ball hits another billiard ball that was at rest: part (or all) of the kinetic energy from the first ball is transferred to the second ball.

## History of kinetic energy

The origin of the adjective kinetic comes from the Greek word kinesis, which means movement. The dichotomy between kinetic energy and potential energy goes back to Aristotle's concepts of actuality and potentiality.

The first relationship between mass energy and speed in classical mechanics was developed by Gottfried Leibniz and Johann Bernoulli, who described kinetic energy as the living force. Later, Gravesande de Willem from the Netherlands provided experimental evidence of this relationship. By dropping weights from different heights on a clay block, Gravesande de Willem determined that its depth of penetration was proportional to the square of its impact velocity. Émilie du Châtelet recognized the implications of the experiment and published an explanation.

The terms kinetic energy and work in their current scientific meanings date back to the mid-19th century. The first to understand these was Gaspard-Gustave Coriolis, who in 1829 published the article entitled Du Calcul de l'Effet des Machines outlining the mathematics of kinetic energy. William Thomson, later Lord Kelvin, is credited for coining the term "kinetic energy."