**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.

Power is the product of force and velocity. The power input to a gear train with a torque *T _{A}* applied to the drive pulley which rotates at an angular velocity of

*ω*is

_{A}*P=T*.

_{A}ω_{A}Because the power flow is constant, the torque *T _{B}* and angular velocity

*ω*of the output gear must satisfy the relation

_{B}which yields

This shows that for an ideal mechanism the input-output speed ratio equals the mechanical advantage of the system. This applies to all mechanical systems ranging from robots to linkages.

Read more about this topic: Leverage

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