# 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 = 1/2mv2

• 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 = 106 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 × 106 J of energy.
• 1 kilowatt hour of electrical energy is commonly known as 1 unit.