WorkWork: Work is said to be done when the point of application of a force moves and it is measured using the product of force and the distance moved to the direction of the force.

In equation form,

Work done = Force Distance Moved

The SI unit of work is the Joule(J)

W= F SWhere,W=Work doneF=Constant Force(in Newton's)S=Distance moved to the direction of force(meters)

A man is pushing against a solid wall but the wall remains stationary.

A man is pushing a car and the car moves to the left.

Holding a heavy set of weights above your head.

(to the direction of the force)

WorkJoule: 1 Joule of work is done when a force of 1 Newton moves a distance of 1 meter.

A person is pushing a trolley in a supermarket. If the force, applied by him on the trolley is 30N, and the trolley moves a distance of 5m in the direction of the force, calculate the work done.

1 Joule = 1 Newton 1 Meter; 1J = 1Nm

W = F S

= 30 5

=150J ans

Here,

F=30N

S= 5 m

W= ?

Work(on Gravitational Force): Suppose the mass of an object is “m” and height is “h”.Work = Force Distance

=Fh

=mghAn object is being lifted from the floor onto a table top, which is 2m above the ground. If the lifting force F is 20N, calculate the work done.

m

h

W = F S

= 20 2

=40Jans

Here,

F =20N

S =2m

W =?An electric motor is used to lift a 5kg mass through 3m, calculate the work done by the motor.

W = F h

= mg h

= 5 10 3

= 150Jans

Here,

m =5kg, h=3m

g=10N, W=?

EnergyEnergy: Energy is the capacity of a body to do work.

The SI unit of energy is Joule(J)

Chemical Energy

Some forms of energy

Sound Energy

Light Energy

Heat Energy

Electrical Energy

Nuclear Energy

Mechanical Energy

Solar Energy

Magnetic Energy

Chemical Energy: It releases energy as a result of a chemical reaction (e.g. burning of fuel), combustion of food in the body. Example: Oil, Wood, Coal, Battery, Food.

Sound Energy: Sound is a form of energy that is passed from one point to another as a wave. Sound is produced by vibrating source placed in a media. The media is usually air, but it can be any gas, liquid or solid.

Light Energy: Light is electromagnetic spectrum that can be detected by the human eye. Light travels in straight lines. We see something that give off their own light (for example the Sun). There are also other things that use daylight or other light. They reflect light into our eyes(for example, this page). Light carries energy. Light wave can travel through empty space.

Heat Energy: Heat is one kind of energy, that is used to know if a matter is cold or hot. With many chemical reactions, heat is produced, sometimes, however, the reverse happens and heat energy is taken in from the surroundings.

Electrical Energy: Electrical energy is important to all of us. Electricity is used to transfer energy from one place to another. Electricity current is a flow of electric charge.

Nuclear Energy: Atomic bombs, nuclear reactors

Mechanical Energy: I) Kinetic energy II) Potential Energy

Solar Energy: Solar system is one of the main sources of energy. The sun radiates huge amounts of energy,a tiny fraction of which falls on the earth. Two main energies that we get from the sun are heat and light.

Potential Energy: Potential Energy is the energy stored by a body by virtue of its position or condition. For example:

An object raised above the ground has gravitational potential energy by virtue of its raised position

Rubber band has elastic potential energy by virtue of its condition.

Some type of P.E. Example of where stored

Gravitational P.E Water held behind a dam

Chemical P.E Food and Fuels

Elastic P.E Rubber Band

Nuclear P.E Particles in an atomic nucleus

Gravitational Potential Energy (G.P.E): This is the energy gained by an object if lifted up against the force of gravity.

Calculation of G.P.E:

G.P.E = Mass Gravitational Field Strength Height

= m g h

I) Find force needed to lift object

II) Multiply this by distance lifted

III) This gives work done in lifting object from the ground

IV) This equal P.E is gained by object

Kinetic Energy (K.E): Kinetic energy is the energy owned by a body by virtue of its motion. Any moving object has Kinetic Energy.

Kinetic Energy (K.E)=

For two objects of the same mass at different speeds, the faster object has the greater K.E. Similarly,for two objects of different masses but moving at the same speed,the object of the greater mass has greater K.E

Here,

Ek =Kinetic Energy(in J)

m =Mass of the body(in kg)

v =Speed of the body(in m/s)

2SpeedMass21

2mv21

kE

Law of Conservation of EnergyLaw of Conservation of EnergyEnergy can neither be created nor destroyed in any process. It can be converted from one form to another, but the total amount remains constant.

Wasted Energy: It is found that the energy output is always less then than energy input. This is mainly due to the work which must be done against frictional force. So we can write:

Energy Input = Useful Energy Output + Wasted Energy Output

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

The SI Unit of Power is Watt(W)

taken Timedone WorkPower

1 kilowatt(kW) = 1000 watts(103 W)

1 megawatt(MW)= 1000000 watts(106W)

taken TimeTransferEnergy Power or

tE

tWP Here,

P = Power

W = Work done

E = Energy converted

t = Time taken

Second 1Joule 1 watt1 SJ /1 W1 in symbol

Efficiency is a ratio. It has no units. We can also express it as percentage multiplying by 100%

Explain the statement: “The efficiency of the power station is about 30%”

InputEnergy TotalOutputEnergy UsefulEfficiency

Ans: It means that in a power house it is found that during the series of transfers of energy, about 70% of the energy input is wasted and lost as terminal energy. Only about 30% of the energy input is finally converted into the useful energy.

Efficiency: The ratio between useful energy output to the total energy input is called efficiency.