Force Ratio
The force ratio is the load force versus the effort force.
A machine is a device that can change the magnitude and line of the action of force.
Examples of machines are
 pulley systems
 gear systems
 screwjacks
A simple machine amplifies the input (effort) force to a larger output (load) force. The force ratio can be expressed as
F_{r} = F / S (1)
where
F_{r} = force ratio  mechanical advantage
F = load force (N, lb_{f})
S = effort force (N, lb_{f})
Example  Force Ratio for Pulley
The effort force for a pulley with 4 ropes, no friction loss (μ = 1) and load 100 kg is calculated to 245 N.
The force ratio can be estimated to
F_{r} = (100 kg) (9.81 m/s^{2}) / (245 N)
= 4
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