Energy | Work and Energy | Class IX

The capacity or ability of a body to do work is called energy.
The S.I. unit of energy is Joule.

EXAMPLE: A man or a horse does work when they pull a load.

Our lifestyle demands energy in various forms. Some forms of energy available naturally or created artificially are follows:

1. Heat or Thermal energy: The energy possessed by a body due to its temperature is known as heat or thermal energy.

2. Chemical energy: The energy released in chemical reactions is known as chemical energy.

3. Sound energy: The energy of a vibrating body producing sound is known as sound energy.

4. Electrical energy: The energy of moving electrons in a conductor connected with a battery is known as electrical energy.

5. Nuclear energy: The energy released when two nuclei of light elements combine with each other to form a heavy nucleus or when a heavy nucleus breaks down into two light nuclei is known as nuclear energy.

6. Solar energy: The energy radiated by the sun is known as solar energy.

7. Mechanical energy: The energy possessed by a body because of its speed or position or change in shape is called the mechanical energy. It is the sum of kinetic energy and potential energy of a body.
M.E.= K.E.+ P.E.

a. Kinetic energy: The energy possessed by a body by vertue of its motion is called kinetic energy.
K.E.= mv2/2

b. Potential energy: The energy possessed by a body on account of its position or configuration, is called potential energy.
P.E. = mgh


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