Energy
Energy is the capacity to do work.
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Energy is the capacity (or capability) to do work.
Energy is used or consumed when work is done.
The SI unit for energy is joule - J, where
1 J = 1 Nm
which is the same unit as for work.
Imperial Units of Energy
- 1 J = 0.738 ft lb
- 1 ft lb = 1.356 Nm (J)
Energy forms
There can be several forms of energy, including
- mechanical energy
- heat or thermal energy
- electrical energy
- chemical energy
- nuclear energy
- light energy
Energy Efficiency
Energy efficiency is the ratio between useful energy output and input energy, and can be expressed as
μ = Eo / Ei (1)
where
μ = energy efficiency
Eo = useful energy output
Ei = energy input
It is common to state efficiency as a percentage by multiplying (1) with 100.
Example - Energy Efficiency
A lift moves a mass 10 m up by exerting a force of 100 N. The input energy to the lift is 1500 J. The energy efficiency of the lift can be calculated as
μ = 100 (N) 10 (m) / 1500 (J)
= 0.67 or
= 67 %
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