Kinetic Energy

1. [Mohan Basnet, Gauhati University, Guwahati-781014 Assam, India]

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1. Physics
2. Energy
3. Kinetic Energy
Kinetic Energy
Kinetic energy is the measure of the work that an object does by virtue of its motion. Simple activities like
walking, jumping, throwing, and falling involve kinetic energy. In this article, let us familiarise ourselves with
the concept of kinetic energy.

Table of Contents

 What is Kinetic Energy?

 Kinetic Energy Units

 Kinetic Energy Examples

 Kinetic Energy Transformation

 Kinetic Energy Formula

 Kinetic Energy Equation Derivation

 Kinetic Energy: a scalar or a vector?

 Kinetic Energy Calculation

 Kinetic Energy Types

 Radiant Energy

 Thermal Energy

 Sound Energy

 Electrical Energy

 Mechanical Energy

 Overview of Kinetic Energy

 Difference Between Kinetic and Potential
Energy
  Frequently Asked Questions – FAQs

What is Kinetic Energy?

To accelerate an object, we have to apply force. To apply force, we need to do work. When work is done on an
object, energy is transferred, and the object moves with a new constant speed. We call the energy that is
transferred kinetic energy, and it depends on the mass and speed achieved.
The kinetic energy definition in Physics is given as:

Kinetic energy of an object is the measure of the work an object can do by virtue of its
motion.
Kinetic energy is a scalar quantity, and it is entirely described by magnitude alone.

Units 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.

Kinetic Energy Examples

 A 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 a 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 its large mass and speedy velocity.

Kinetic Energy Transformation

Kinetic energy is transferred between objects and can be transformed into other forms of energy. Yo-Yo is a
great example to describe the transformation of kinetic energy. While beginning to play with it, one starts by
letting it rest in hand; at this point, all the energy is stored in the ball in the form of potential energy. Once the
person drops the yo-yo, the stored energy is transformed into kinetic energy, the energy of movement. Once the
ball reaches the bottom of the yo-yo, all the energy is converted to kinetic energy.

Similar Reading:
Scalar quantity Potential energy

The Formula for Kinetic Energy

The kinetic energy equation is given as:

KE=12mv2
Where KE is the kinetic energy, m is the body’s mass, and v is the body’s velocity.

Deriving Kinetic Energy Equation

Kinetic energy equation can be obtained by the basic process of computing the work (W) that is done by a
force (F). If the body of mass m was pushed for a distance of d on a surface by applying a force that’s parallel
to it, then the work done would be:
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.vf2−vi22d=m.vf2−vi22d=12.m.vf2−12.m.vi2

Simplifying the equation further, we get

K.E=12mv2

Alternately, one can say that the total work that is done on a system is equivalent to the change in kinetic
energy. This statement is equated as follows:
Wnet=ΔK

This equation is known as the work-energy theorem and has large applications even if the forces applied vary
in magnitude and direction.
Read More: Derivation Of Kinetic Energy

Is Kinetic Energy a Vector or a Scalar Quantity?

In the expression, we see that velocity (v) is squared. We know that the square of a vector quantity is a scalar,
and we also know that mass is a scalar quantity. Therefore, kinetic energy is a scalar quantity.

Kinetic Energy Calculation

1. Calculate the kinetic energy of a 200 kg object that is moving at a speed of 15 m/s.
Solution:
The kinetic energy of the body can be calculated using the following equation:
KE=12mv2

Substituting the values in the above equation, we get

KE=12(200kg)(15m/s)2

KE=45000Jor45KJ
2. Calculate the mass of the object moving at a speed of 40 m/s and having a kinetic energy of 1500 J.
Solution:
Rearranging the kinetic energy equation, we get
m=2KEv2

Substituting the values in the above equation, we get,

m=2×1500402=1.87kg

Types of Kinetic Energy

There are five types of kinetic energy: radiant, thermal, sound, electrical and mechanical. Let us look at some
of the kinetic energy examples and learn more about the different types of kinetic energy.

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

 Ultraviolet light
 Gamma rays

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

 Hot springs
 Heated swimming pools

Sound energy
The vibration of an object produces sound energy. Sound energy travels through the medium but cannot travel
in a 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 be destroyed but converted from one form to another. Examples of mechanical energy are:

 Orbiting of satellites around the earth

 A moving car
Read more: Law of Conservation of Energy

Overview of Kinetic Energy

Kinetic Energy Kinetic energy is the measure of the
Definition work an object can do by the virtue
of its motion.

Kinetic Energy KE=12mv2

Equation

Kinetic Energy The SI unit of kinetic energy is Joules

Units which is equal to kg-m2s-2

Kinetic Energy A river flowing at a certain speed

Examples

Kinetic Energy Radiant energy, Thermal energy,

Types Sound energy, Electrical energy and
Mechanical energy.

Difference Between Kinetic Energy and Potential Energy

Kinetic energy Potential energy
 Kinetic energy is a form Potential energy is the
of energy possessed by form of energy possessed
an object due to its by an object due to its
motion. position or state.

Formula used is
The formula used is mgh
KE=12mv2

Vibrational energy is Gravitational potential

an example of kinetic energy is an example of
energy potential energy

Read More: Difference between Kinetic and Potential Energy

For more information on kinetic energy and potential energy, watch the below
videos:

9,92,194
11,626

Related Links

 What Is Energy?
 What is Energy Conversion?
 Relation BetweenKinetic Energy and
Momentum

Frequently Asked Questions – FAQs

Q1

What is the definition of kinetic energy?

The kinetic energy is the measure of the work an object can do by virtue of its motion.

Q2

Can the kinetic energy be negative?

The kinetic energy cannot be negative because the square of the speed gives a non-negative number, and the
mass cannot be negative.

Q3
When is the kinetic energy maximum?
The kinetic energy is maximum when the potential energy is minimum, and this occurs when the velocity is
maximum and the mass is at the equilibrium position.

Q4

What happens to the kinetic energy when the speed decreases?

When the speed decreases, the kinetic energy will be transformed into potential energy, thermal energy or other
forms of energy.

Q5

How is the kinetic energy different from the potential energy?

The energy possessed by the body by virtue of its position is known as potential energy. The energy possessed
by the body by virtue of its motion is known as kinetic energy.

The below video provides Work and Energy quiz

3,959

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