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Chapter 5

Chapter 5. Machine. Can be simple or compound Device that makes work easier by: Increasing force applied to object (carjack) Increasing distance over which force is applied (rake) Changing direction of applied force (ax in wood)

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Chapter 5

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  1. Chapter 5

  2. Machine • Can be simple or compound • Device that makes work easier by: • Increasing force applied to object (carjack) • Increasing distance over which force is applied (rake) • Changing direction of applied force (ax in wood) You do work ON a machine and the machine does work on the object

  3. 2 forces when a machine is used to do work: • Input force: force applied TO machine = Fin • Output force: force applied BY machine = Fout • Work done on machine = Win • Work done by machine = Wout • Cannot create energy, so Wout is NEVER greater than Win (lost as heat, friction, etc.) • Ideal machine: perfect, no friction, 100% efficient • Win = Wout ***IF Fin is applied over greater distance than the Fout is exerted over (car jack, ramp, crowbar, claw hammer)

  4. Mechanical Advantage • Ratio of Fout to Fin • Calculate: MA = Fout (N) Fin (N) Ex: What is the MA of a hammer if the input force is 125N and the output force is 2000N?

  5. Efficiency • Measurement of how much work put into a machine is changed into useful output by a machine • Increase efficiency = less heat from friction • Calculate: eff % = Wout (j) Win (j) x100%  Real machines always > 100%

  6. Simple Machines: Lever • Bar that pivots around a fulcrum • Input & output arms • Fout depends on lengths of input & output arms • 3 classes: 1st fulcrum between I and O Ex: see-saw, scissors 2nd fulcrum at end, I at other Ex: wheelbarrow 3rd fulcrum at end, I in middle Ex: tweezers, hockey stick, broom

  7. Pulley • Grooved wheel with a rope, chain, cable running along • Axle acts as a fulcrum • 3 types • Fixed: attached, flag pole • Movable: wheel free, multiples force • Block & Tackle: fixed & movable together

  8. Wheel & Axle • Axle attached to center of larger wheel that rotate together, doorknobs, screwdrivers Inclined Plane • Sloping surface that reduces amount of force • Fin exerted over a longer distance

  9. Screw • Inclined plane wrapped around a post, tiny ramp, jar lids, anything with threads Wedge • Inclined plane with 1 or 2 sloping sides • Changes direction of Fin • Knife, ax blade

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