Machines  Help people do work  DOES NOT DECREASE the AMOUNT of work done—makes work easier!  CHANGES the way work is done: Size of force Distance over which force is applied Direction force is exerted

Machines  Powered by energy Electrical (computers); mechanical (rake) Transfer energy to the objects on which work is done  Input force Force exerted on machine  Output force Force machine exerts on object

Machines Output force Input force Changes a large force over a short distance to a small force over a larger distance

Mechanical Advantage  The # of times a machine multiplies a force  MA = output force input force (MA = OF/IF)

Mechanical Advantage  Less force over a greater distance:  MA > 1 ; OF > IF (doorknob)  Ex: IF = 10N OF = 40N MA = 4

Mechanical Advantage  Greater force over shorter distance:  MA < 1 ; OF < IF (rake)  Ex: IF = 10 N OF = 5 N MA =.5

Mechanical Advantage  Change ONLY the direction of the force  Input force and output force are the same!  MA = 1; IF = OF (flag)

Mechanical Advantage  The output force of a machine is 600 N and the input force is 200 N.  What is the mechanical advantage of the machine?

Mechanical Advantage  A machine has an input force of 150 N and a mechanical advantage of 0.5.  What is the output force?

Mechanical Advantage  The output force of a machine is 135 N, and the mechanical advantage is 2.5.  What is the input force?

Energy and Work SHORT ROUTE = MORE FORCE & LESS DISTANCE LONG ROUTE = LESS FORCE & MORE DISTANCE

Efficiency  Input work Work you do on the machine  Output work Work machine does  Efficiency (Always expressed as a %) Ratio of output work to input work Ideal = 100%; lose efficiency due to friction E (%) = OW / IW X 100

Efficiency  NO MACHINE IS 100% EFFICIENT--friction  More moving parts…more friction…less efficiency Car engine 25% Electrical motor 80%  Increase efficiency…oil parts

LEVER Rigid bar that is free to pivot, or rotate, about a fixed point  Fixed point is called the fulcrum  Multiplies IF or changes direction

Simple Machines  3 classes of levers IF OF IF OF IF

LEVER  First class Multiply force Multiply distance Changes the direction of the input force

 FULCRUM IN MIDDLE!  IF same as EFFORT  OF same as LOAD or RESISTANCE  Examples: seesaws, scissors, pliers, crowbar, head tilting

LEVER  Second Class Always multiplies force Does NOT change direction of the input force

 OF IS IN THE MIDDLE!  Examples: bottle opener, nutcracker, doors, wheelbarrow, oar, ball of foot used to raise body

LEVER  Third class Multiplies distance

 IF IS IN THE MIDDLE!  Used to decrease distance over which IF applied or to increase speed end of lever  Examples: baseball bat, fishing pole, shovels, catapults, hoe, scythe, arm

WHEEL & AXLE Wheel attached to a shaft Rotating collection of levers; axle at the wheel’s center is fulcrum Ex: screwdriver---handle is wheel, shaft is axle  Doorknob, car steering wheel  Multiply force; exert over a longer distance (circular distance)

PULLEY Grooved wheel with rope wrapped around it Fixed pulley: attached to a structure; changes direction; IMA = 1 Ex: raising a sail

PULLEY Movable pulleys  Multiplies force  Exert a force over a greater distance  IF & OF are in the same direction  Useful when moving an object from above  2 rope sections = ½ force than a fixed pulley; pull 2 x distance

PULLEY  Block & tackle Combination of fixed and moveable pulley

INCLINED PLANE Flat, slanted surface Exert IF over longer distance; multiplies distance IF < OF Less steep = less force & more distance

WEDGE Thick end & thin end Cuts, splits, pierces objects; holds objects together Inclined plane that moves to do work Thin wedges have small angles- ---need less IF than thick  Why sharp knives cut easier than dull

 SINGLE: Doorstop Chisel Ice scraper Teeth (incisors)  Double Axe Knife

SCREW Inclined plane wrapped around a cylinder Closer the threads are, the greater the MA  Multiplies distance IF on the screw, OF on wood Ex: jar lid, faucet

Mechanical Advantage  Ideal mechanical advantage: assume machine is 100% efficient  Lever IMA = distance from IF to fulcrum / distance from OF to fulcrum  Wheel & Axle IMA = radius of input / radius of output  Inclined plane IMA = length of incline / height of incline

COMPOUND MACHINE 2 or more simple machines Ex: mechanical pencil shapener Gears  Based on wheel & axle  Have teeth  MA = Total MA of all the simple machines  Micromachines/nanotechnology