mechanical engineering

Energy is the capacity or capability to do work and energy is used when work are done.

The unit for energy is joule J, where
1 J = 1 Nm

which is the same unit as for work.

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 with 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 %