Machines A device that makes work easier A tool containing one or more parts that uses energy to perform an intended action. make work easier by allowing us to push or pull over increased distances. Increases force applied Changes direction of force

In vs. Out Input force – force applied to the machine Fin Output force – force applied by the machine Fout Work = Force x distance Work in = Fin x distance Fin exerted Win Work out = Fout x distance Fout exerted Wout

Ideal Machines? All work in = work out Win = Wout Fin x din = Fout x dout No energy is “lost” to friction or elsewhere Does NOT exist!! Every real machine has friction Win ≠ Wout Input is always greater than output Win = Wout + Wfriction

Efficiency Measure of how much input is used for useful work output Efficiency (%) = work output x 100 Wout x 100 work input Win - Always less then 100 % in a real machine - Output is always less than input due to frictional losses

The input work you do on a can opener is 24 J The input work you do on a can opener is 24 J. The output work the can opener does is 18 J. What is the efficiency of the can opener? Efficiency = ( output / input ) x 100 Eff = (18 J / 24 J ) x 100 Eff = 75 %

What is the input work when the output work is 2841 J and the efficiency is 15 %? Efficiency = (output/ input ) x 100 15 % = ( 2841 J / input ) x 100 0.15 = ( 2841 J / input ) (input)(0.15) = (2841 J/input )( input ) (input)( 0.15 ) = 2841 J Input = 2841 J / 0.15 Input = 18 940 J

Mechanical Advantage Measure of the force amplification achieved by using a tool, mechanical device or machine system. How much easier and faster a machine makes your work Mechanical advantage = output force RMA = Fout input force Fin Ideal Mechanical Advantage – IMA mechanical advantage of an ideal machine (no friction) IMA = input distance output distance

An input force of 120 N is applied to a machine to move a 720 N box An input force of 120 N is applied to a machine to move a 720 N box. What is the mechanical advantage of the machine. Mechanical advantage = output force / input force MA = 720 N / 120 N MA = 6

Using a set of pulleys, a mover raises a load a distance of 5 m by pulling in 20 m of cord. What is the ideal mechanical advantage of the system. IMA = input distance / output distance IMA = 20 m / 5 m IMA = 4