# PSEB 9th Class Science Notes Chapter 11 Work, Energy and Power

This PSEB 9th Class Science Notes Chapter 11 Work, Energy and Power will help you in revision during exams.

## PSEB 9th Class Science Notes Chapter 11 Work, Energy and Power

→ All living beings need food for their energy needs.

→ Machines too need fuels like petrol and diesel for energy.

→ In our daily life, we consider any useful physical or mental activity as work.

→ Work done by the force acting on a body is equal to the product of the magnitude of the force and the displacement in the direction of the force.

→ When a force acts in a direction opposite to the direction of displacement produced, then the work done is negative.

→ When a force acts in the direction of displacement then the work done is positive.

→ For us, the sun is the major natural source of energy.

→ In addition to this, we can also get energy from nuclei of atoms, from the interior of earth, and tides.

→ If a body has the capacity to do work then it is said to possess energy.

→ The object which does work loses energy and the object on which work is done gains energy.

→ The sum total of potential and kinetic energy of the body is called mechanical energy.

→ The energy present in the body due to its motion is called it’s kinetic energy.

→ The kinetic energy of an object increases with the increase of its velocity.

→ When an object is raised to some height above the ground, the work done against gravitational force is stored in the object as potential energy.

→ We can transform one form of energy into another form.

→ The rate of doing work or transformation of energy is called power.

→ The unit of energy is joule but this unit is small. Its bigger unit is kilowatt hour (kWh) 1 kWh = 3.6 × 106 J

→ HP Energy consumed in industries and commercial establishments are expressed in kilowatt-hour which is also called unit (B.O.T. unit)

→ In order to survive all living beings have to do some basic activities for which energy is required. This energy they get from the food they eat.

→ According to the law of conservation of energy, energy can neither be created nor destroyed but it can only be transformed from one form to another form total energy before and after transformation always remains constant.

→ Energy is present in different forms as for example kinetic energy, potential energy, heat energy, chemical energy, electric energy, and light energy.

→ From a scientific point of view for doing work two conditions must be satisfied:

• some force must act on the object
• the object must be displaced in the direction of the force.

→ The unit of power is the watt.

→ 1 kilowatt = 1000 watt.

→ 1 watt is the power of that agent which does 1 joule of work in 1 second.

→ Energy: The capacity of doing work is called energy.

→ Kinetic Energy: The capacity of the bodies to do work due to the motion present in them is called kinetic energy.

→ Potential Energy: The capacity of an object to do work clue to change in its position or configuration is called its potential energy.

→ Law of Conservation of Energy: Energy can neither be created nor destroyed but it can be changed from one form into another form.

→ Joule: If one Newton (N) of force acts on a body of 1 kg and displaces it through 1 m then work done on the body is one joule.

→ Power: The rate at which energy is supplied or consumed is called power. The unit of power is the watt (W).
Power = $$\frac{\text { Energy Supplied }}{\text { Time }}$$

→ Watt: If a source supplies or consumes energy at the rate of 1 Joule (J) per second then the power of the source, is said to be one watt.

→ Work: If the force acting on a body displaces the body in the direction of force then work is said to be done by the force.
Work = Force × Displacement
i.e. W = F × S