 # Kinetic Energy

A force must be applied on a body to accelerate an object. Work must be done in order to apply a force. The body will move with an unvarying speed after the work has been done due to the energy provided by it. The speed and the mass of the body are factors on which the energy transfer that makes up the kinetic energy depends.

Just like all forms of energy, Kinetic energy too can be transformed into other forms of energy and transmitted among the objects. For instance, a moving car may hit a stationary person and then the kinetic energy of the car gets transferred into the person’s body.

## What is Kinetic Energy?

The kinetic energy of an object is the energy that it possesses due to its motion. Kinetic energy definition is given as:

The energy of an object because of its motion or the energy gained by an object from its state of rest to motion.

### How is kinetic energy different from potential energy?

Kinetic energy is due to an object’s motion whereas potential energy is due to an object’s position or state. Velocity is an important factor while calculating an object’s kinetic energy. However, velocity has nothing to do with an object’s potential energy.

Check the video below to understand how kinetic energy is different from potential energy. ## Formula of Kinetic Energy

Following is the formula of kinetic energy:

 $KE=\frac{1}{2}mv^{2}$

Where,

• KE is the kinetic energy of the object
• m is the mass of an object
• v is the velocity of an object

Kinetic energy is an example of scalar quantity which means that the quantity has only magnitude and no direction.

### Unit of Kinetic Energy

• The SI unit of kinetic energy is Joule which is equal to 1 kg.m2.s-2.
• The CGS unit of kinetic energy is erg.

Also, check: Derivation Of Kinetic Energy

## What are the Examples of Kinetic Energy?

• A semi-truck travelling down the road has more kinetic energy than a car travelling at the same speed because the truck’s mass is much more than the car’s.
• A river flowing at a certain speed comprises kinetic energy as water has certain velocity and mass.
• The kinetic energy of an asteroid falling towards earth is very large.
• The kinetic energy of the aeroplane is more during the flight due to large mass and speedy velocity.

## What are the Types of Kinetic Energy?

If something is moving, it has kinetic energy. The faster the motion of the object, the more kinetic energy it has. Following are the five types of kinetic energy:

Radiant energy is a type of kinetic energy as it is always in motion travelling through medium or space. Examples of radiant energy are:

• Ultraviolet light
• Gamma rays

### Thermal energy

Thermal energy is also known as heat energy which is generated due to quick motion of atoms when they collide with each other. Examples of thermal energy are:

• Hot springs
• Heated swimming pool

### Sound energy

Sound energy is produced by the vibration of an object. Sound energy travels through the medium but cannot travel in vacuum as there are no particles to act as a medium. Examples of sound energy are:

• Tuning fork
• Beating drums

### Electrical energy

Electrical energy is obtained from the free electrons that are of positive and negative charge. Examples of electrical energy are:

• Lightning
• Batteries when in use

### Mechanical energy

The sum of kinetic energy and potential energy is known as mechanical energy which can neither be created nor destroyed but can be converted from one form to other. Examples of mechanical energy are:

• Orbiting of satellites around the earth
• A moving car

## Difference between Kinetic Energy and Potential Energy

The difference is given in the table below. To check the detailed kinetic and potential energy difference visit the link.

 Kinetic energy Potential energy Kinetic energy is defined as the energy present in an object from the state of rest to motion Potential energy is defined as the energy contained in an object by the virtue object’s position Formula used is $KE=\frac{1}{2}mv^{2}$ The formula used is mgh Vibrational energy is an example of kinetic energy Gravitational energy is an example of potential energy

You may also want to check out these topics given below!

### How to Calculate Kinetic Energy?

Simply put, Kinetic energy can be calculated by the basic process of computing the work (W) that is done by a force (F). If the body has a mass of m that was pushed for a distance of d on a surface with a force that’s parallel to it.

$W=F.d=m.a.d$

The acceleration in this equation can be substituted by the initial (vi) and final (vf) velocity and the distance. This we get from the kinematic equations of motion.

$W=m.a.d\\ \\ =m.d.\frac{v_{f}^{2}-v_{i}^{2}}{2d}\\ \\ =m.\frac{v_{f}^{2}-v_{i}^{2}}{2d}\\ \\ =\frac{1}{2}.m.v_{f}^{2}-\frac{1}{2}.m.v_{i}^{2}$

Kinetic Energy’s (K) basic quantity ½mv2 changes when a particular sum of work is acted upon an object.

$K.E=\frac{1}{2}mv^{2}$

The total work that is done on a system is equivalent to the change in kinetic energy. Thus,

$W_{net}=\Delta K$

This equation is known as the work-energy theorem and has large applications even if the forces applied to vary in magnitude and direction. This factor is an important one in the concept of conservation of energy.

### Kinetic Energy Facts – What’s Interesting?

The equation tells us some interesting things about kinetic energy:

• The velocity of a body when squared is dependent on the kinetic energy. This tells us that when the velocity of a body is doubled the kinetic energy gets quadrupled. If two cars, one travelling at 60mph and the other at 30mph the kinetic energy of the former car is four times that of the latter. Thus, the possibility of death increases by about four times too!
• Kinetic energy cannot be negative; it must either be zero or positive. Velocity can be negative or positive but kinetic energy is at all times positive.
• Kinetic energy is not a vector unit. The direction of a projectile does not matter. What matters is the velocity it’s thrown with.

## Frequently Asked Questions on Kinetic Energy

### What is the definition of kinetic energy?

Kinetic energy or KE of an object is the energy that it possesses due to its motion. It can be defined as the work needed to accelerate a body of a given mass from rest to its stated velocity.

### What are 5 kinetic energy examples?

• Some kinetic energy examples are given below:
• A bullet fired from a gun
• Boiling water
• Riding a bike
• A flowing river