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CONSTRUCTIVE THOUGHTS Simple Machines 7.2
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Six Types of Simple Machines leverpulley wheel and axle inclined plane screwwedge
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Lever A bar free to pivot about a fixed point fulcrum = fixed point effort arm = part of lever where F e is applied resistance arm = part of lever where F r is applied
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The Mechanical Advantage of Levers MA lever = length of effort arm (L e ) length of resistance arm (L r ) Problem: A worker uses an iron bar to raise a manhole cover weighing 65 N. The effort arm of the lever is 60 cm long, and the resistance arm is 10 cm long. What is the MA of the bar?
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First class: multiply force and/or direction Second class: multiply force Third class: cannot multiply force; MA < 1 = increases speed Three Types of Levers R E F RE F RE F
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Examples of Class Three Levers
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Pulley grooved wheel with rope/chain running along groove fixed or movable: –fixed: changes direction; MA = 1 –movable: multiplies force; MA = 2 »block and tackle: system of fixed and movable pulleys
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Wheel and Axle 2 wheels of different sizes that rotate together –F e applied to larger wheel –smaller wheel (axle) exerts F r MA = radius of wheel (r w ) radius of axle (r a ) »Problem: A steering wheel with a 24 cm radius turns the column with a 4 cm radius. What is the MA?
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Gears modified wheel-and-axle machines wheel with teeth along edge –larger gear=effort gear –smaller gear=resistance gear
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Inclined Plane a sloping surface used to raise objects Work is same, but distance is increased, so force is less MA = length of slope (l) height of slope (h)
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Screw An inclined plane that wraps in a spiral around a post Threads form a tiny ramp
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Wedge An inclined plane with one or two sloping sides examples: chisels, knives, ax blades, etc. difference from ramp: the wedge is what moves through material Identify as many simple machines as possible in the following clip:
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