**Work**

**Work** is done when a **force** produces **motion** in a body.

Work done in moving a body is equal to the product of force exerted on the body and the distance moved by the body in the direction of the force.

**Work = Force X Distance****W=FS**

- Work is a
**scalar**quantity. It has only magnitude and no direction. - Its SI unit is
**joule**(J). **One joule of work**is said to be done on an object when a force of 1 N displaces the object by 1 m along the line of action of force.- Work done by a force can be positive, negative or zero.
- It is
**positive**when a force acts in the direction of motion of the body. - It is
**negative**when a force acts opposite to the direction of motion of the body. - It is
**zero**when a force acts at right angles to the direction of motion of the body.

**Energy**

- We define energy as the
**ability to do work**. - The amount of energy possessed by a body is the amount of work it can do when that energy is released.
- Energy is a
**scalar**quantity. - Its SI unit is
**joule**(J). 1 kJ = 1000 J - The main forms of energy are kinetic energy, potential energy, chemical energy, heat energy, light energy, sound energy, electrical energy and nuclear energy.

**Kinetic Energy**

- The energy possessed by a body on account of its
**motion**is known as**kinetic energy**. - Kinetic energy possessed by a body of mass ‘m’ moving with a velocity ‘v’ is given by the formula:

**Kinetic Energy = 1/2mv ^{2}**

- Kinetic energy of a body is directly proportional to o the
**mass**of the body - the
**square of the velocity**of the body

**Potential Energy**

- The energy possessed by a body because of its
**position**or**configuration**is known as**potential energy**. - The work done in raising an object from the ground to a point against gravity is called gravitational potential energy.
- Potential energy of a body of mass ‘m’ raised to a height ‘h’ above the surface of the Earth is given by the formula:

**Potential Energy = m g h**

*where ‘g’ is the acceleration due to gravity.*

#### Law of conservation of energy:

*Energy can neither be created nor destroyed; it can only be converted from one form to the other.*

- Sum of kinetic energy and potential energy of an object is its total mechanical energy.

# Power

Power is defined as the rate of doing work or the rate of transfer of energy.

- Power is a
**scalar**quantity. Its SI unit is**watt**(W). - It is said to be one watt when the rate of consumption of energy is 1 Js
^{−1}. - Larger units of power are
**kilowatt**(kW),**megawatt**(MW) and**horsepower**(hp).**1 kW = 1000 W****1 MW = 10**^{6}W**1 hp = 746 W**

**Commercial Unit of Energy**

- The commercial unit of energy is
**kilowatt hour**(kWh). - One kilowatt hour is the amount of electrical energy consumed when an electrical appliance with a power rating of 1 kilowatt is used for 1 hour.
- 1 kWh is equal to 3.6 × 10
^{6}J of energy. - 1 kilowatt hour of electrical energy is commonly known as
**1 unit**.