# Force Ratio

## Force ratio - load force versus 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
- screw-jacks

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 *