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Chapter 4: Section 2

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Machine- device that makes doing work easier ◦ They change the way a person does work, not the amount of work that needs to be done

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When using a machine, the output work can never be GREATER than the input work ◦ A machine cannot do more work than you put in! ◦ Law of conservation of energy ◦ Do not get work confused with force!

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MA = output force = Newtons input force Newtons Or: MA = F out F in The UNITS cancel out!

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F in = Input force- the effort, or force you exert on a machine F out = Output force-the force exerted by the machine

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Changing the amount of force needed Changing the distance the force covers Changing the direction of the force

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◦ Some machines allow you to exert a smaller force over a longer distance ◦ Output force > input force, resulting in a MA > 1 ◦ Ex: a ramp Output force = 500N = 10 Input force 50N

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Some machines allow you to exert your force over a shorter distance Output force < Input force, resulting in a MA < 1 ◦ Ex. A rake Output force = 10N = 0.1 Input force 100N

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Some machines allow you to change the direction of the input force Output force = input force, resulting in MA = 1 Ex. pulley Output force = 50N = 1 Input force 50N

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Efficiency = output work input work x 100% Or: Eff = Wout x 100% Win Answer will always be in a percentage!

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W out = 4500 J W in = 7500 J Eff = _____ Eff = Wout x 100% Win Eff = 4500 J x 100% 7500 J Eff = 0.6 x 100% Eff = 60%

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Friction – reduces efficiency by converting some work into heat. ◦ The efficiency of a real machine is always less than 100% because of friction. ◦ Only ideal machines are 100% efficient Oil, or another lubricant can increase efficiency by reducing the number of contact points between surfaces.

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