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# Kinetic Energy and Potential Energy

Molecular kinetic energy of gases toward subsist is made up of a huge quantity of modest molecules. Rapidly moving molecules forever collide with each other and also against the container wall, raising the overall kinetic energy of the molecules contained inside.

The molecules move slowly if the temperature is kept under control or within standard limits while the velocity of the molecules increases with increase in temperature
Energy is available in several different forms. These different forms of energy can be converted from one form to another. Some common forms of energy are mechanical energy, chemical energy, heat energy, sound energy, light energy, electrical energy and atomic or nuclear energy. Mechanical energy includes kinetic and potential energy.

The energy by virtue of which a body can do some mechanical work directly is called mechanical energy.
As discussed the common forms of mechanical energy are:
Kinetic energy
Potential energy
We can also say that,
Mechanical energy = Kinetic energy + Potential energy

 Related Calculators Elastic Potential Energy Calculator Gravitational Potential Energy Calculator Potential Energy Calculator Calculate Kinetic Energy

## Kinetic Energy Definition

Flowing flood water can wash away huge structures like railway lines and bridges. Water flowing out of a dam can run a turbine to generate electricity. The wind blowing during a storm can up-root big trees. The blowing wind can also run the blades of a wind mill and can be used to produce electricity or for doing some mechanical work. Thick sheets of metal and logs of wood, a fast moving bullet can penetrate the human body, etc.Thus, we see that all moving bodies can do some work, which means all moving bodies 'posses’ energy.
Kinetic Energy Definition
"The energy possessed by a body by virtue of its motion is called kinetic energy. Kinetic energy is denoted by the abbreviation K.E. So a moving body can do some work due to its kinetic energy."
Various forms of Kinetic Energy
A moving body can have three types of motion. These are
1. Translational motion
2. Rotational motion
3. Vibrational motion
• Translational Kinetic Energy
A body moving in a straight line path is said to exhibit translational motion. Therefore, the kinetic energy of a body by virtue of its motion along a straight path is called translational kinetic energy.

Example: A person walking on the road, a freely falling object, a ball rolling on the floor, etc., possess translational energy.
• Rotational Kinetic Energy

When a body rotates on its axis, it is said to possess rotational motion. The kinetic energy of a body by virtue of its rotational motion is called rotational kinetic energy.

Example: The moving blades of a ceiling fan, a spinning top, a potter’s wheel, etc., possess rotational kinetic energy.

• Vibrational Kinetic Energy

Small and rapid to-and-fro motion of a body about its mean position is called vibrational motion. The kinetic energy of a body by virtue of its vibrational motion is called vibrational kinetic energy.

Example: Vibrating the string of a guitar, a tuning fork struck against a rubber block, etc., possess vibrational kinetic energy.

• Formula of Kinetic Energy
The kinetic energy of a body having mass m and velocity v is equal to $\frac{1}{2}$ mv2. We can write it as:
K.E. = $\frac{1}{2}$ mv2

## Kinetic Energy of a Molecule

Under low temperature, the molecules would contain less kinetic energy as kinetic energy by virtue of the velocity of molecule will have less energy contained within. The molecules contained within reflect average kinetic energy and thus the overall energy of the container will also be low.

Gases undergo pressure factor as the particle are continuously bounced off the walls of the container, and as these collisions are elastic in nature, the energy is transferred to the container wall.

Force = mass x (velocity)2

or

F = mv2

Whatever may be the substance, solid, liquid or gas; they will have some amount of temperature contained within but not anything like the heat of absolute zero.

The individual part of a material is heated better than an additional part as the energy of the molecule within the heated part would be larger in comparison to the cooler part.

### Kinetic Energy

• Motion energy: It is the energy of any object in motion including wind and water waves.
• Sound energy: Sound is produced when a substance vibrates on application of force. Sound travels through a medium through waves and therefore has motion associated with it.
• Radiant energy: Electromagnetic energy including light and solar energy moves in the form of waves. Solar energy provides light and warmth.
• Thermal energy: It is due to the vibration and movement of the atoms and molecules in a substance.

### Potential Energy

• Chemical Energy: Energy present in the bonds between atoms and molecules.
• Mechanical energy: Energy form stored in objects due to tension (elastic bands, spring).
• Nuclear energy: It is the energy that holds an atomic nucleus together.
• Gravitational energy: Energy due to position or height.
• Electrical energy: Energy stored in a battery.

### Formula for calculations

Kinetic energy = ½ x m (mass) x v2 (velocity)
Potential energy = m (mass) x g (gravity) x h (height)

Kinetic Energy Examples

Examples of Kinetic energy has Describe Below:-

• Flowing flood water can wash away railway lines and bridges.
• Water flowing out of a dam can run a turbine to generate electricity.
• The wind during a storm can uproot big trees.
• The moving wind can run the blades of a wind mill and can be used for producing electricity or for doing some mechanical work.

### Solved Examples

Question 1: A man of 50 kg climbs to the top of a building which is 40 m high. What is the potential energy of the man?
Solution:
Weight of the man = mass x gravity
= 50 kg x 9.8 m/s2 = 490 N
Gravitational Potential energy (GPE) = weight x height
= 490 N x 40 m = 19600 J = 19.6 kJ

Question 2: The kinetic energy of a car is found to be 40,000 J. What velocity is the car traveling if its mass is 10,000 kg
Solution:
Kinetic energy (KE) = ½ mv2
40,000 = (½) x (10,000 kg ) x ( v2)
v2 = (2 ) x (40,000 ) = 8
10, 000
v = 2.8 m/s

## Average Molecular Kinetic Energy

The molecules of any substance, normally warm, are measured with the help of Boltzmann allocation rule. As these molecules are constantly on the move, and the average translational kinetic energy is considered from their sum total energy and the total number of molecules present,

f(E) = A $-\frac{E}{kT}$

Energy of an organization by virtue of its motion is recognized as the kinetic energy.

The moving wind, a moving bullet, moving water, all possess kinetic energy. Moving wind can work in turning the blades of a wind mill, moving water can work in turning a turbine to generate electricity. A moving bullet can penetrate even a steel plate due to its high velocity. The kinetic energy of an organization is capability of responsibility effort.

The kinetic energy of a given set of molecules is nothing but the combined effort of the molecules and to measure kinetic energy, it is described as the product of its individual mass with the square of its velocity.

In other words, Kinetic energy (K) = $\frac{1}{2}$ mv2

Where m is mass of body (in kg) and v is velocity of body (in m/s).

## Potential Energy

Potential energy is defined as follows: Energy possessed by a body by virtue of its position, which means the height above the ground, or configuration, which refers to its shape, is called potential energy.

There are actually two types of potential energies, namely
1. Gravitational potential energy
2. Elastic potential energy
Gravitational Potential Energy

The potential energy of a body by virtue of its height above ground level is called gravitational potential energy. For example, the energy stored in a body, held at a certain height above the ground is gravitation potential energy.

Elastic Potential Energy

The potential energy of a body by virtue of its configuration (or shape) is called elastic potential energy. For example, the potential energy stored in the coiled spring of a clock is elastic potential energy. Potential energy is abbreviated as P.E. The unit of potential energy is Joules.

The formula that is used to calculate the potential energy is P.E. = mgh, where m is the mass of the body, g is the acceleration due to gravity and h is the height of the body from the ground level. This generally refers to the gravitational potential energy.

### Examples of Potential Energy

Examples of Potential energy has Describe Below:-
• Water stored in an overhead tank.
• A body held at a certain height above ground level
• The coiled spring in a watch or clock.
• A stretched rubber band.
• A compressed or stretched steel spring.

## Kinetic vs Potential Energy

Certain bodies may possess both kinetic and potential energies at the same time. Some examples are given below:
• A man climbing a hill
• A flying aeroplane
• A bird flying in the sky
• A body rolling down a hill

### Potential Energy to Kinetic Energy

When a body falls from a certain height it loses potential energy and gains kinetic energy. Thus, when a body falls from a certain height, the potential energy of the body changes into kinetic energy.

This is explained as follows:

A body held at a certain height is at rest. Thus, at this stage, it has only potential energy due to its height from the ground. When it is dropped, it gains speed and starts moving downwards. As the body moves downwards, its potential energy decreases due to decrease in the height and its kinetic energy increases due to increase in its speed. When the body reaches the ground, its height from the ground is zero.

So, the potential energy of the body on reaching the ground becomes zero and the whole of it gets converted into kinetic energy. Thus when a body falls from a certain height, the potential energy gradually changes into kinetic energy.

### Kinetic Energy to Potential Energy

When a body is thrown up, its velocity gradually decreases as it goes up due to the downward pull of the earth. As a result, its kinetic energy decreases and its potential energy increases gradually as the body goes up.

This continues until at a certain height, the kinetic energy of the body becomes zero. At this point, the body has maximum potential energy. So, when a body is thrown up, its kinetic energy decreases and the potential energy increases, because its kinetic energy gradually changes into potential energy.
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