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) You do work ON a machine and the machine does work on the object

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)

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?

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%

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

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

Wheel & Axle Inclined Plane 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

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