2Simple MachinesS8P3. Students will investigate the relationship between force, mass, and the motion of objects.c. Demonstrate the effect of simple machines (lever, inclined plane, pulley, wedge, screw, and wheel and axle) on work.
3WorkIn science, the word work has a different meaning than you may be familiar with in your everyday life.The scientific definition of work is:The transfer of energy when a force moves an object over a distance in the same direction of the force.Energy: the ability to do workIf no movement happens, no work is done.Work = force x distance (W = Fd)Measured in newton-meters or joules (J)Examples: pushing a shopping cart, turning a door knob, kicking a soccer ball, lifting a box
4Work or Not WorkA scientist delivers a speech to an audience of his peers.NoA bodybuilder lifts a dumbbell above his head.YesA student pushes against a wall that does not move.A father pushes a baby in a carriage.A woman carries a grocery bag to her car.
5Simple Machines Simple Machine A device that makes work easier by changing the size and/or the direction of the force used to do the work.A simple machine does not help you to do less work.Work with a simple machine = Work without a simple machineNo machine can increase both the magnitude of the force and the distance an object travels at the same time.Therefore, there is a trade-off between force and distance.
6Work Work Input (Win) work done on a machine Work Output (Wout) work done by a machine
7Win = Wout Win > Wout Work Law of Conservation of Energy Energy can never be created or destroyed.Energy can be transformed from one form to another.You can never get more work out than what you put in.In an ideal machine...In a real machine...some energy (output force) is given off (“lost”) as friction.Win = WoutWin > Wout
8Mechanical Advantage (MA): number of times a machine multiplies the effort force
96 Kinds of Simple Machines Inclined Plane FamilyInclined PlaneWedgeScrewLever FamilyLeverPulleyWheel and Axle
10How does the Simple Machine Make Work Easier for You? Inclined PlaneInclined PlaneA straight, slanted surface used to raise objects because it is higher on one endExample: Ramps, stairs, laddersHow does the Simple Machine Make Work Easier for You?The Effects on WorkMechanical AdvantageInclined planes: You use less effort force over a longer distance.The longer the inclined plane = smaller effort force needed = easier workMA greater than 1 (MA > 1)hl
11Wedge Wedge A moving inclined plane with 1 or 2 sloping sides Examples: knives, hatchets, ax blade, blades of scissors, nails, teeth, plow, and chiselA wedge transfers force in one direction into force in two directions.Wedges are used to split or cut things apart.
12How does the Simple Machine Make Work Easier for You? ScrewScrewA screw is an inclined plane wrapped around a shaft or cylinder.Examples: a fastener (screw), jar lid, top of jar, drill bit, light bulb, viseThe inclined plane allows the screw to move itself when rotated.How does the Simple Machine Make Work Easier for You?The Effects on WorkMechanical AdvantageScrews: You use less effort force over a longer distance.The closer the threads on the screw = longer the inclined plane = smaller effort force needed = easier workMA greater than 1(MA > 1)
13Lever Lever a bar that pivots at a fixed point called a fulcrum “Give me a place to stand and I will move the Earth.”– ArchimedesEngraving from Mechanics Magazine, London, 1824ResistancearmEffort armFulcrum
14The 3 Classes of LeversThe class of a lever is determined by the location of the effort force, the load, and the fulcrum.Effort force (input force): the force applied to the leverLoad (output/resistance force): the object being moved
15Lever Mechanical Advantage (MA) Effort arm length(input force)Resistancearm length(output force)Le must be greater than Lr in order to multiply the force.
16Lever First Class Lever fulcrum is located between the effort force and resistance force (load)can increase force, distance, or neitheralways changes the direction of force (i.e. a downward effort force on the lever results in an upward movement of the resistance force)Examples: crowbars, scissors, pliers, tin snips, shovels, and seesaws
17Lever Second Class Lever the load (resistance) is located between the fulcrum and the effort forcealways increases effort forcedoes not change the direction of forceeffort force moves farther than resistanceWhen the load is located closer to the fulcrum than to the effort force, an increase in force (mechanical advantage) results.Examples: nut crackers, wheel barrows, doors, and bottle openers
18Lever Third Class Lever the effort force is applied between the fulcrum and the resistance force (load)always increases the distance that the effort force travelsdoes not change the direction of forcealways produce a gain in speed and distance and a corresponding decrease in forceExamples: arm, tweezers, hammers, baseball bats, brooms, and rakes
19How does the Simple Machine Make Work Easier for You? PulleyPulleygrooved wheel with a rope or chain running along the groovea “flexible first-class lever”a load is attached to one end of the rope and a force is applied to the other endLeFLrHow does the Simple Machine Make Work Easier for You?The Effects on WorkMechanical AdvantagePulleys: Your effort force changes direction and/or you use less effort force over a longer distance.Your effort force changes direction = easier workAND/ORMore pulleys = smaller effort force needed = easier workMA equal to 1 (MA = 1)MA greater than 1 (MA > 1)
20Pulley Mechanical Advantage equal to the number of supporting ropes MA = 0MA = 1MA = 2
21Pulley Fixed Pulley MA = 1 does not increase force changes direction of force
22PulleyMovable PulleyMA = 2increases forcedoes not change direction
23Pulley Pulley System/Block & Tackle MA = 4 combination of fixed and movable pulleysincreases forcemay or may not change direction
24Wheel and Axle Wheel Axle Wheel and Axle two wheels of different sizes that rotate togetherthe wheel is always larger than the axlea pair of “rotating levers”Examples: door knob, gears, car axle, pencil sharpener, screw driver, faucet handlesWheelAxle
25How does the Simple Machine Make Work Easier for You? Wheel and AxleWhen effort is applied to move the wheel, the axle turns a shorter distance, but moves with more force.The larger the wheel is when compared to the axle, the larger the mechanical advantage.How does the Simple Machine Make Work Easier for You?The Effects on WorkMechanical AdvantageWheel and Axles: You use less effort force over a longer distance when turning the wheel.The larger the wheel = smaller effort force needed = easier workMA greater than 1 (MA > 1)