Mechanical efficiency is a fundamental concept in physics that measures how well a machine converts input work into useful output work. Every machine has some energy loss due to friction and other factors, making efficiency less than one hundred percent.
Mechanical efficiency is defined as the ratio of useful work output to total work input, expressed as a percentage. The formula is eta equals useful work divided by total work, times one hundred percent. This diagram shows how total input work is divided into useful work and wasted energy.
To understand mechanical efficiency, we need to distinguish between different types of work. Useful work is the work that accomplishes the intended task, like lifting a load. Total work is all the energy input to the machine. The difference between them is wasted work, which includes energy lost to friction, heat, and other inefficiencies.
Let's work through a practical example. A motor uses one thousand joules of energy to lift a fifty newton weight by fifteen meters. The useful work equals force times distance, which is fifty newtons times fifteen meters, equals seven hundred fifty joules. The efficiency is seven fifty joules divided by one thousand joules, times one hundred percent, which equals seventy five percent.
In reality, mechanical efficiency is always less than one hundred percent due to unavoidable energy losses. These include friction between moving parts, heat generation, sound and vibration, and air resistance. While we can design machines to minimize these losses, we cannot eliminate them completely. This is why perfect efficiency remains an ideal that real machines can approach but never achieve.