Chapter 5 Machine Can be simple or compound

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 125 N and the output force is 2000 N?

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) x 100% 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: 1 st fulcrum between I and O Ex: see-saw, scissors 2 nd fulcrum at end, I at other Ex: wheelbarrow 3 rd 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 • 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