Efficiency vs..

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Presentation transcript:

Efficiency vs.

Efficiency is a measure of how much energy is wasted by a machine. Machines are useful because they allow us to use less force over a longer distance to do the same work.

Machines always waste some energy. The 2nd Law of Thermodynamics states that whenever work is done, some energy is converted to heat. Therefore: Win > Wout Work in: Energy supplied to the machine. Work out: Work actually done by machine.

The efficiency of a machine is: Efficiency = Wout x100% Win or There are no units for efficiency, it is simply expressed as a percentage. Efficiency = Pout x100% Pin

Example: A lever is used to lift a 50.0 kg object 10.0 cm. To do this we must apply a force of 75 N to the end of the lever which displaces 1.00 m. Find the efficiency. 75 N 1.00 m 50.0 kg 50.0 kg 0.100 m