8.4 Mechanical Advantage and Efficiency

Notes

Mechanical advantage (MA) tells how many times a machine multiplies your input force.

• $\displaystyle \text{MA} = \frac{\text{output force}}{\text{input force}}$. A 300 N load lifted with a 50 N effort gives $\text{MA} = 6$.
• Ideal MA of an inclined plane $\displaystyle = \frac{\text{length}}{\text{height}}$. A 4 m ramp rising 1 m has an ideal MA of 4.
• Ideal MA of a lever $\displaystyle = \frac{\text{effort arm}}{\text{load arm}}$.
• Efficiency $\displaystyle = \frac{\text{work output}}{\text{work input}} \times 100\%$. Friction makes real efficiency less than 100%.
• Example: 80 J out for 100 J in is 80% efficient.