Efficiency is a comparison of how much work goes INTO a machine versus how much work COMES OUT of a machine. How is efficiency expressed? in kilograms as a percentage (\%)

Efficiency is typically expressed **as a percentage (%)**. It quantifies how effectively a machine converts input work into output work. The formula for calculating efficiency is: \[ \text{Efficiency (\%)} = \left( \frac{\text{Output Work}}{\text{Input Work}} \right) \times 100 \] For example, if a machine uses 100 joules of input energy and produces 80 joules of useful output energy, its efficiency would be: \[ \text{Efficiency} = \left( \frac{80}{100} \right) \times 100 = 80\% \] This means that 80% of the input energy is effectively converted into useful work, while the remaining 20% may be lost to factors like heat, friction, or sound. **Key Point:** Efficiency is commonly expressed as a percentage to easily compare the performance of different machines or systems.