Force Ratio
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
- screw-jacks
A simple machine amplifies the input (effort) force to a larger output (load) force. The force ratio can be expressed as
Fr = F / S (1)
where
Fr = force ratio - mechanical advantage
F = load force (N, lbf)
S = effort force (N, lbf)
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
Fr = (100 kg) (9.81 m/s2) / (245 N)
= 4
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• Mechanics
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