1. Energy
Energy: Energy is the capacity of a body to do work.
The SI unit of energy is Joule(J)
Some forms of energy
 Chemical Energy
 Light Energy
 Sound Energy
 Heat Energy
 Electrical Energy
 Nuclear Energy
 Mechanical Energy
 Solar Energy
 Magnetic Energy

2. 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.
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.
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.

3. 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.

4. Example of where stored
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

5. Gravitational Potential Energy (G. P
Gravitational Potential Energy (G.P.E): This is the energy gained by an object if lifted up against the force of gravity.
G.P.E = Mass  Gravitational Field Strength  Height
= m  g  h
Calculation of G.P.E:
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

6. 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)=
Here,
Ek = Kinetic Energy(in J)
m = Mass of the body(in kg)
v = Speed of the body(in m/s)
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

7. Law of Conservation of Energy
Energy 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

8. Power: Power is defined as the rate of transfer of energy or work done.
Here,
P = Power
W = Work done
E = Energy converted
t = Time taken
The SI Unit of Power is Watt(W)
in symbol
1 kilowatt(kW) = 1000 watts(103 W)
1 megawatt(MW) = watts(106W)

9. Efficiency is a ratio. It has no units
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%”
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.