What Is Kinetic Energy?

In classical mechanics, an object's kinetic energy is the energy it possesses due to being in motion.

What is kinetic energy?

Kinetic energy definition: The amount of work required to accelerate a body of a given mass to a certain speed. This energy will be constant as long as the velocity of the body is maintained.

Depending on the movement, we can distinguish two types:

  • The translational kinetic energy, in which the object describes a linear trajectory.

  • The rotational kinetic energy, in which the object rotates on itself.

The joule (J) is the SI unit of energy,

What Is the Kinetic Energy Formula?

The kinetic energy equation is as follows:

Definition and formula of kinetic energy 


  • m is the mass in kilograms (kg)

  • v is the speed expressed in meters per second (m / s)

The relativistic kinetic energy is approximated well by the classical when the rate is much lower than the speed of light.

The formula for the rotational kinetic energy of a body rotating on an axis is the following:

 Definition and formula of kinetic energy


  • Ix: Moment of inertia.

  • ω: The angular velocity (how fast an object rotates or revolves relative to another point).

The total kinetic energy is equal to the sum of both equations.

What Is the Relationship Between Kinetic and Potential Energy?

In nature, there are many forms of energy. Energy cannot be created or destroyed, but it can be transformed from one type to another.

A particular case is these two types of energy: the sum of the two is mechanical energy.

Potential energy is the mechanical energy associated with a body's location within a force field, for example, the force of gravity.

If an object is at a certain height, it has gravitational potential energy (which depends on the elevation). If we drop it, it loses potential energy and is transformed into kinetic energy (energy of motion).

Examples of Kinetic Energy

We can observe this type of energy on a day-to-day basis:

1.- Man on a Skateboard

A man on a skateboard experiences kinetic energy. A skateboarder with a higher body mass will acquire higher energy, and one whose skateboard allows him to go at higher speeds.

2.- Thrown Ball

By printing our force on a ball at rest, we accelerate it enough so that it travels the distance between a playmate and us. Thus, we are giving it kinetic energy that then, when tackling it, our partner must counteract with a work of equal or greater magnitude.

3.- A Roller Coaster

A roller coaster cart (moving object) gains speed as it falls and increases in speed. Moments before it begins its descent, the coach will have potential and not kinetic energy. Still, once the movement starts, all potential energy becomes kinetic and reaches its maximum point as soon as the fall ends.

This energy will be more incredible if the cart is full of people than empty (it will have more mass).

4.- Cycling

A cyclist who is at the starting point, without exerting any type of movement, has a coefficient of kinetic energy equivalent to zero. However, once you start pedaling, this energy increases. Thus, the higher the speed, the greater the kinetic energy.

Once the moment to brake has arrived, the cyclist must slow down and exert opposing forces to decelerate the bicycle and settle back into an energy coefficient equal to zero.

5.- Hydroelectric Generating Plants.

Hydropower uses large waterfalls or river falls, which guarantee a constant flow of moving water. Hydroelectric plants generate electric energy due to the kinetic energy contained in the impact of water on turbines.


Published: September 25, 2014
Last review: October 15, 2020