•      The ability to do work is called energy.

•      There are many forms of energy.


Mechanical energy:

•      The energy which is possessed by an object due to its motion or its stored energy of position is called mechanical energy.

•      Mechanical energy can be either kinetic energy (energy of motion) or potential energy (stored energy of position).

For example:

Figure 29: For example, a moving car possesses mechanical energy due to its motion (kinetic energy)

A moving baseball possesses mechanical energy due to both its high speed (kinetic energy) and its vertical position above the ground (gravitational potential energy)

A book at rest on the top shelf of a locker possesses mechanical energy due to its vertical position above the ground (gravitational potential energy)

A barbell lifted high above a weightlifter's head possesses mechanical energy due to its vertical position above the ground (gravitational potential energy)

•      Any object which possesses mechanical energy - whether it is in the form of potential energy or kinetic energy - is able to do work.

Figure 30: The water stored behind a dam has potential energy, which gets converted to kinetic energy as the water falls down


Electrical energy:

•      It is a secondary energy source which means that we get it from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources.

For example:

Figure 31: All appliances use electrical energy

•      Electricity's extraordinary versatility as a source of energy means it can be put to an almost limitless set of applications like transport, heating, lighting, and communications.

Figure 32: Limitless applications of electricity

Figure 33: Limitless applications of electricity


Light energy:

•      Light energy helps us to see the things around us.

For example:

Figure 34: Halogen lights are used in sports

Figure 35: Some sources of light energy

Figure 36: Various appliances of light using light energy


Heat energy:

•      In our homes, we use heat energy to cook food.

Figure 37: Burning fuels such as LPG and kerosene used in lamp releases heat energy


Sound energy:

•      When an object moves quickly, it compresses the surrounding air, giving that air, potential energy. For example, the head of drum.

For example:

Figure 38: Sources of sound energy

Figure 39: Sources of sound energy


Wind energy:

•      Wind is air in motion. It is produced by the uneven heating of the earth’s surface by the sun.

Figure 40: Uneven heating of the earth’s surface by the sun

•      Since the earth’s surface is made of various land and water formations, it absorbs the sun’s radiation unevenly.

•      When the sun is shining during the day, the air over landmasses heats more quickly than the air over water.

•      The warm air over the land expands and rises, and the heavier, cooler air over water moves in to take its place, creating local winds.

•      At night, the winds are reversed because the air cools more rapidly over land than over water.

For example:

Figure 41: Windmill used to generate electrical energy, kite flying due to wind, table fan works on the same principle

•      Windmills work because they slow down the speed of the wind.

•      The wind flows over the airfoil shaped blades causing lift, like the effect on airplane wings, causing them to turn.

•      The blades are connected to a drive shaft that turns an electric generator to produce electricity.

•      Today’s wind machines are much more technologically advanced than those early windmills.

•      They still use blades to collect the wind’s kinetic energy, but the blades are made of fiberglass or other high-strength materials.

•      Large turbines are connected to the utility power network - some other type of generator picks up the load when there is no wind.

•      Small turbines are sometimes connected to diesel/electric generators or sometimes have a battery to store the extra energy they collect when the wind is blowing hard.