# Energy - Potential Kinetic And Internal Energy

## What is Energy?

* Energy* is defined as the capacity to do work.Energy is transferred one object to another in different forms. It is a property of a substance by which the object is capable of doing work.S.I. unit of energy is joule

There are different forms of energy in the world but following two types of energy are main in any system.

1. Stored Energy

2. Transit Energy or Energy in transition form

### 1. Stored Energy

**Stored energy** is defined of a substance which is limited within the system boundaries.The potential energy.kinetic energy,internal energy,chemical energy,nuclear energy are the example of stored energy.It is also Thermo-Dynamic property.

### 2. Transit Energy

It is a form of energy which is capable of crossing the system's boundaries.Example of transit energy is heat,work,electrical energy.

## ☛ Types Of Stored Energy

Now we are going to discuss three types of stored energy.

1. Potential Energy

2. Kinetic Energy

3. Internal Energy

### 1. Potential Energy

The energy possessed by a body by virtue of its position is called its **potential energy** and is given by following equation:

Let,

W = Weight of the body

m = Mass of the body

z = Distance through which the body falls,

g = Accreration due to gravity = 9.81 m/s^{2}

∴ Potential energy,

If may be noted that,

a)When W is in newtons and z in metres, then potential energy will be in N-m.

b)When m is in kg and z in metres,then the potential energy will also be in N-m,then

Potential Energy,

### 2. Kinetic Energy

The energy possessed by a body by virtue of its motion is called its * kinetic energy* and is given by following equation:

Let,

m = mass of the body

V = Velocity of the body

When m is in kg and V is in m/s,then kinetic energy will be in N-m,

We know that kinetic energy,

### 3. Internal Energy

**Internal energy** is the energy possessed by a body or a system due to its moleculer arrangement and motion of its molecules.It is usually represented by U.The intenal energy is expressed in joule.

The change of internal energy when the substance passes from state 1 to state 2 can be expressed

The total energy of the system (E) is equal to the sum of the three types of energies.

Mathematically,

For the unit mass, above expression can be expressed as:

When the system is stationary and the effect of gravity is neglected,then PE=0, and KE=0.In such case,

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