Editing Mechanical advantage (section)

== Speed ratio ==
{{main|Speed ratio}}
The requirement for power input to an ideal  mechanism to equal power output provides a simple way to compute mechanical advantage from the input-output speed ratio of the system.

The power input to a gear train with a torque ''T<sub>A</sub>'' applied to the drive pulley which rotates at an angular velocity of ''ω<sub>A</sub>'' is ''P=T<sub>A</sub>ω<sub>A</sub>''.

Because the power flow is constant, the torque ''T<sub>B</sub>'' and angular velocity ''ω<sub>B</sub>'' of the output gear must satisfy the relation
:<math>P = T_A \omega_A = T_B \omega_B, \!</math>
which yields
:<math> \mathit{MA} = \frac{T_B}{T_A} = \frac{\omega_A}{\omega_B}.</math>
This shows that for an ideal mechanism the input-output speed ratio equals the mechanical advantage of the system.  This applies to all [[mechanical system]]s ranging from [[robot]]s to [[linkage (mechanical)|linkages]].