# Kinetic energy: definition, types, formulas and examples

In classical mechanics, the kinetic energy of an object is the energy it possesses due to being in motion and having mass. The greater the speed of an object and the greater its mass, the greater its kinetic energy.

Kinetic energy is also defined as the amount of work required to accelerate a body of a certain mass up to a certain speed. This energy will be constant as long as the speed of the body is maintained.

This form of energy is important in various contexts. For example, in the physics of crashes and collisions, it is used to analyze the energy transformations that occur during the event.

In addition, it is essential in fields such as mechanics, engineering and industry, since it allows us to understand and take advantage of the movement of objects for different applications and technologies.

Kinetic energy is measured in joules (J) according to the international system of units.

## Types of kinetic energy

Kinetic energy can be classified into different types depending on the context or the source of motion. Here are some examples of types of kinetic energy:

1. Linear: It is the energy associated with the rectilinear movement of an object along a trajectory.

2. Rotational: Refers to the energy associated with the rotational movement of an object around an axis. This type of energy is applied to objects that rotate, such as wheels, turbines, or frisbees.

3. Vibrational: It is the energy associated with the vibratory movement of an object. It applies to systems that oscillate or vibrate, such as guitar strings, molecules in a gas, or particles in a wave.

4. Thermal: It is the energy associated with the random movement of particles in a system. It is related to the temperature of the object and is due to the fast and constant movement of atoms or molecules. The higher the temperature of an object, the greater its thermal kinetic energy.

5. Kinetic energy of subatomic particles: In the field of particle physics, subatomic particles, such as electrons, protons, or neutrons, possess energy due to their motion. This type of energy is especially relevant in nuclear reactors since the probability of generating nuclear fission reactions depends on the speed of free neutrons.

6. Fluid Kinetic Energy: In fluid mechanics, kinetic energy relates to the motion of a fluid, such as a liquid or gas.

Each of the types mentioned above has a different formula to be calculated. In this section we will mention the linear and curl formulas.

### Linear Translational Kinetic Energy Formula

The formula that is applied for objects that move in a straight line is the following:

Where:

• m is the mass in kilograms (kg)

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

From this formula, it can be seen that the kinetic energy is directly proportional to the square of the velocity. This means that an object moving at a higher speed will have a much higher kinetic energy than an object of the same mass but with a slower speed.

In relativistic mechanics it is a good approximation only when the speed is much less than the speed of light.

### Rotational Kinetic Energy Formula

For the calculation of a body rotating on an axis is the following:

Where:

• Ix: moment of inertia.

• ω: Angular speed.

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.

## 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).

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Data de publicació: September 25, 2014
Última revisió: June 29, 2023