Kinetic and potential energy

The kinetic energy is the energy associated with movement and potential energy is the energy associated with the position in a system. Energy, in general, is the ability to do work.

Both kinetic and potential energy represent the two fundamental types of existing energy . Any other energy is a different version of kinetic or potential energy or a combination of both. For example, mechanical energy is the combination of kinetic and potential energy.

Kinetic energyPotential energy
DefinitionEnergy associated with movement.Energy associated with position in a system.
SI unitsJoule, 1J = kg.m 2 / s 2Joule, 1J = kg.m 2 / s 2
Formulak = m . 2
  • P = mgh (gravitational)
  • el = ½ kx 2 (elastic)
EtymologyFrom the Greek kinetikos: to set in motion.From the Latin potis : capable, possible.
  • Wind
  • Thermal
  • Gravitational
  • Elastic
  • Electrical
  • Chemistry
DependenceAmount of mass and speed.Amount of mass and height (gravitational).

What is kinetic energy?

Kinetic energy is the type of energy that is associated with motion . Anything that is moving has kinetic energy.

In the international system (SI), the unit of kinetic energy is the jouje (J), the same as that of work. One joule corresponds to 1 kg.m 2 / s 2 .

Formula for calculating kinetic energy

The kinetic energy (E k ) can be calculated using the formula:

k = m . 2 ,


  • m corresponds to the mass of the object and
  • v at the speed of the object.

From this formula we can deduce that the kinetic energy depends on the amount of mass and on the speed. Thus, a car at the same speed as a truck has less kinetic energy. On the other hand, a car at 80 km / h has more kinetic energy than one at 40 km / h.

Examples of kinetic energy

In everyday life there are many examples of the use of kinetic energy.


The game of bowling, where a person throws a ball between 3 and 7 kg in order to knock down 10 pins, is based on the kinetic energy carried by the ball, which depends on its mass and the speed it carries.


The wind is nothing but air in motion. The kinetic energy from the movement of the air can be transformed into electrical energy by means of wind turbines.

Thermal energy

Thermal energy is kinetic energy associated with the microscopic motion of the particles in the system. When we heat water or any other object, we are increasing the kinetic energy by heat transfer.

What is potential energy?

Potential energy is the type of energy that is associated with the relative position within a system, that is, the position of one object with respect to another. Two separate magnets have potential energy for each other.

In SI, the unit of potential energy is the jouje (J), as is kinetic energy. One joule corresponds to 1 kg.m 2 / s 2 .

Formulas to calculate potential energy

Gravitational potential energy is the energy due to the position of the object with respect to the Earth’s surface:



  • m is the mass of the object (kilograms),
  • g is the gravitational acceleration constant of the Earth (equal to 9.8 m / s 2 ) and
  • h is the distance (height in meters) between the Earth and the object.

The gravitational energy depends on the mass of the object and the height at which the object is with respect to a reference level.

The formula for elastic potential energy is equal to:

ell =½ kx 2


  • k is the spring force constant and
  • x is the measure of the spring displacement from a starting point to the ending point.

When the distance is zero, that is, the spring has not been stretched, the elastic potential energy is equal to 0.

Examples of potential energy

Among the sources we use to obtain energy, many depend on potential energy. Let’s see.

The energy stored in dams

Water stored in elevated reservoirs, for example in dams, has gravitational potential energy. Falling water transforms its potential energy into kinetic energy, capable of doing work in the turbines at the bottom of the dam. These turbines generate electricity that is distributed to the electrical distribution network of towns and cities.


When a spring is stretched or compressed, it stores an amount of energy in the form of elastic potential energy . When the spring is released, the stored potential energy is transformed into kinetic energy.

Bow and arrow

The bow and arrow is an example of how elastic potential energy is transformed into kinetic energy. When the bowstring is stretched, work is done that is stored as potential energy in the stretched string. By releasing the string, the potential energy of the string is transformed into kinetic energy which is then transferred to the arrow.


Electricity is a form of potential energy determined by the position of charges in a system (the electric field).

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