Machines aren't perfect -- not even close -- if you'd like to measure the efficiency of a machine, you can calculate it. There are all sorts of factors affecting the efficiency of machines, things like friction and the materials the machine is made from.
Efficiency is measured as a percentage. If a fixed pulley with a mechanical advantage of 1 is used to lift a crate, the input force should be exactly equal to the output force. External factors can influence the ideal mechanical advantage of the pulley.
With the fixed pulley, the crate being lifted required 6 Newtons of input force. The actual output force of the fixed pulley is 3 Newtons of force. To calculate the efficiency of the fixed pulley, use the equation:
Efficiency = Output Force / Input Force x 100
Input Force = 6 Newtons
Output Force = 3 Newtons
Efficiency = 3 Newtons / 6 Newtons x 100
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