# Kinetic energy. What is it?

Kinetic energy is the energy contained in a body due to being in motion. The kinetic energy is the amount of work needed 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 change its speed.

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

The unit of measure of kinetic energy in the international system of units is joule (J).

## Power Transformation

Energy can be manifested in many forms, including chemical energy, thermal energy, electromagnetic radiation, gravitational energy, electrical energy, elastic energy, nuclear energy, and rest energy. All 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. To understand this aspect, an example will be useful. A motorist uses the chemical energy provided by the combustion of gasoline in a thermal engine to accelerate the motorcycle up 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 into kinetic energy, the energy of movement, but the process is not completely efficient and produces heat inside the engine.

At a certain point, the rider could use this speed to climb a slope until the bike stayed a few meters higher. At this point, all kinetic energy has become potential energy. If the rider wishes to take advantage of the descent to recover speed, at this time the potential energy will be converting to kinetic energy again.

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

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

## History of kinetic energy

The origin of the kinetic adjective 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 relation between mass energy and velocity in classical mechanics was developed by Gottfried Leibniz and Johann Bernoulli, who described kinetic energy as the living force. Later, Gravesande de Willem of the Netherlands provided experimental evidence of this relationship. By dropping weights from different heights into a block of clay, Gravesande de Willem determined that his depth of penetration was proportional to the square of his impact velocity. Emilie 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-nineteenth century. The first to understand these was Gaspard-Gustave Coriolis, who in 1829 published the article entitled Du Calcul de l'Effet des Machines in which sketches the mathematics of kinetic energy. William Thomson, later Lord Kelvin, is credited with coining the term "kinetic energy."

Last review: August 30, 2017

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