Energy
"Energy of a body is it’s capacity to do work"
Greater the amount of energy possessed by the body, greater the work it will be able to do. All the agents which are able to do work are said to be energetic.
i) A bullet fired into a wall is able to penetrate into the wall by doing work against friction due to its energy.
ii) Fast blowing wind is able to turn a wheel.
iii) A moving vehicle possess energy since it does work against friction and air resistance before coming to rest after the engine is switched off.
iv) Water stored in a dam has energy since it can run the turbines when the water flows down onto the turbines.
The different forms of energy are mechanical energy, light energy, heat energy, sound energy. electrical energy, nuclear energy etc.
In mechanics, we divide mechanical energy into two types, namely
(1) Kinetic Energy (2) Potential Energy.
The dimensional formula for energy is ML2T–2 same as that of work.
SI unit of energy is joule (J)
C.G.S unit is erg.
1J = 107 erg.
Note: The other units of energy are:
\(
1eV \approx 1.6 \times 10^{ - 19} J
\) ; \(
1\,MeV\, \approx \,\,1.6 \times 10^{ - 13} J
\)
\(
1\,cal\, \approx \,4.2J
\) ; \(
1\,Kcal\, \approx \,4200J
\)
\(
1\,KWH\, = \,36 \times 10^5 J\, = \,36 \times 10^{12} erg
\)
Note : Many students think that KWH is the unit of power. But it is the unit of
energy. Usually electrical energy is measured in KWH.