Work and Machines What is a machine? A device that allows you to do work in a way that is easier and more effective How machines can help Machines make work easier by changing: Amount of force you exert Example : Lifting a piano to a moving truck vs pushing it up a ramp Distance over which you exert a force Example: Bicycle, you push the pedals a small distance but the bike moves a large distance Direction in which you exert a force Example: Flag pole, you pull down on the rope but the flag moves up Input vs Output Force Input Force: The force YOU exert on a machine Input Work = Input Force X Input Distance Output Force: The force the machine exerts on an object Output Work = Output Force X Output Distance Mechanical Advantage A machines mechanical advantage is the number of times a machine increases a force exerted on it. MA = Output Force / Input Force Example: You exert 15N of force on a can opener, the can opener exerts an output force of 30N on the can. MA = 30N / 15N = 2 There is no unit for mechanical advantage because it is a multiple. Efficiency of Machine The efficiency of a machine compares the output work to the input work. Efficiency = Output Work X 100% Input Work Real vs Ideal Machines An ideal machine has an efficiency of 100%, but one does not exist In all machines some work is lost due to friction