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Published byVirgil Hodge Modified over 9 years ago
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Simple Machines Work, Mechanical Advantage and Efficiency
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Simple Machines All machines can be classified as or a combination of levers and inclined planes. Manipulates the Law of Conservation of Energy The amount of energy that goes in the machine = to the amount of energy that comes out. Work in = Work out F in x d in = F out x d out
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Machines and Work Machines DO NOT decrease work!!! They change the Force and distance needed to get a certain amount of work done. FdFdFd
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Work Done F in F out d in = 1.75 m d out = 0.25 m Fulcrum/ Pivot point 2000 N 1.75 m F in x d in = F out x d out x=0.25 mxF in 2000 N F in = 0.25 mx2000 N 1.75 m = 286 N
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Mechanical Advantage How much a machine changes the force There are 4 variables F e = “effort force”: how much YOU put in. F r = “resistance force”: force generated by machine. d e = “distance effort”: distance effort must travel i.e. length of a lever’s effort arm. d r = “distance resistance”: distance the resistance must travel i.e. the length of the resistance arm in a lever.
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Mechanical Advantage FeFe FrFr d e d r Fulcrum/ Pivot point
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Ideal Mechanical Advantage Model of a machine in an “ideal” world. No friction or heat loss. Ideal mechanical advantage = distance effort/distance resistance. IMA = d e /d r This is a ratio so there are no units
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Mechanical Advantage In the “real” world energy is lost as friction and heat. Mechanical Advantage = resistance force/effort force MA = F r /F e No units
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Efficiency Work out / Work in x 100 The ratio of a machine’s MA to its IMA determines its efficiency. Efficiency = MA / IMA x 100.
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Levers 3 lever types Class 1 lever: Ex: crowbar FeFe FrFr d e d r Fulcrum/ Pivot point Label F e = “effort force” F r = “resistance force” d e = “distance effort” d r = “distance resistance”
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Levers Class 2 lever: Ex: wheel barrow FeFe FrFr d e d r Fulcrum/ Pivot point Label F e = “effort force” F r = “resistance force” d e = “distance effort” d r = “distance resistance”
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Levers Class 3 lever: Ex: bicep FeFe FrFr d e d r Fulcrum/ Pivot point Label F e = “effort force” F r = “resistance force” d e = “distance effort” d r = “distance resistance”
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Inclined Plane Example: ramp drdr dede FrFr FeFe
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Inclined plane Inclined plane wrapped around a cylinder Lever Variation of wheel and axle More simple machines Wedge: Screw: Wheel and axle: Pulley:
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Height = 0.5 m Height does not change, only the angle.
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Height = 0.5 m Scale reads = 300g Car mass = 500g Length = 0.83 m 30 0
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Height = 0.5 m Scale reads = 3N Car mass = 5N Length = 0.83 m 30 0 Modified test
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Height = 0.5 m Scale reads = 300g Car mass = 400g Length = 0.66 m 30 0
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Inclined Plane Example: ramp Force Distance Force drdr dede FrFr FeFe
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Mechanical Advantage Example 200 N 75N 1 m 4 m FeFe FrFr d e d r
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500 N
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Class 3 leverClass 1 leverClass 2 lever FeFe FrFr dede drdr FeFe FeFe FeFe FrFr FrFr FrFr drdr drdr drdr dede dede dede
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ForceResistance Fulcrum
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