chapter 14 work, power and machines d d f f chapter 14.1
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Chapter 14Work, Power and Machines
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dFChapter 14.1
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WorkWork Requires Motion The force must act in the same direction that the object moves. If there is no movement, no work is done.
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Work depends on direction!!
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Work depends on direction!!No Work!!
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Work depends on direction!!
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WorkWork = Force X distanceW = F X dW = Newton X meter = NmW = Joule (J)
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WFdW =FdF =d =
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PowerPower =
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WPtW =PtP =t =
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Increase PowerIncrease work done in same time.
Same amount of work in less time.
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PowerPower =P == Watts= W
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ExampleYou exert a vertical force of 72N to lift a box to a height of 1.0m in a time of 2.0s. How much power is used to lift the box?
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Given: F =72N d=1.0 mt = 2.0sFind: P =? Equation: P = W/t w = FdP = Fd/tSolve: P = (72N x 1.0m)/2.0sP = 36 J/s = 36 W
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James Watt - Horsepower1 horsepower is equal to 746 watts
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HomeworkWorksheet: 14-1Due: 4/5/10
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MachinesCan machines decrease work???Work = Force X distanceChapter 14.2
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Machines do Work
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Machines do WorkChange the size of a force needed The direction of a force. The distance over which a force acts. Machines make work easier to do.WorkForce=distanceX
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Increasing Force
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Direction of Force
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Distance the force acts.
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Work Input and Work Output
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Work Input and Work Output
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Work Input and Work OutputBecause of friction, the work done by a machine (output work) is always less than the work done on the machine (input work).
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Work Input to a machineThe force you exert on a machine is called the input force.
The distance the input force acts through is known as the input distance
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Work Input to a machine
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Work Output from a machineThe force exerted by a machine is called the output force.
The distance the output force acts through is known as the output distance.
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Work Output from a machine
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HomeworkWorksheet: 14-2Due: 4/5/10Worksheet: 14-1
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Chapter: 14-3Mechanical Advantage AndEfficiency
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ActualMechanical AdvantageActual Mechanical Advantage (MA) The number of times a machine multiplies the Input Force.
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ActualMechanical Advantage FO FI
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Output Force - FO Input Force - FI
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ActualMechanical AdvantageMA = Output Force Input force MA = FO FI
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Experiment
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IdealMechanical Advantage(IMA) IMA of a machine is the mechanical advantage in the absence of friction.
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IdealMechanical Advantage
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Ideal Mechanical Advantage - IMAIMA = Input Distance Output Distance MA = DI DO
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Experiment
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MA ExampleExample: Mr. Clune is trying to move a large stone in his yard. He uses a crow bar that gives him a Mechanical Advantage of 100. If the stone weighs 1000N, what force must Mr. Clune apply to move it?
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Given: MA = 100 Fr = 1000NEquation: Fe = Fr MASolve: Fe = 1000N 100Fe = 10N Find: Fe = ?
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EfficiencyThe measure of how much work put into a machine is changed to useful work put out by the machineWorkInput(WIN)WorkOutput(WOUT)
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WOUT WINEfficiency = X 100%
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Experiment
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Example: A sofa weighing must be placed in a truck bed off the ground. A worker uses a force of to push the sofa up an inclined plane that has a slope length of What is the of the inclined plane?1500N1.0m500N4.0m.efficiency
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l = 4m(DI)h = 1m (Do)
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Given: Fo = 1500N Do = 1.0m FI = 500N DI = 4.0mFind: Efficiency = ?Efficiency = 75%
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HomeworkWorksheet: 14-3Math Practice:Page: 425 1-3Page: 426 8-9Due: 4/7/10
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A student working in a grocery store after school pushes several grocery carts together along a ramp. The ramp is 3meters long and rises 0.5meter. What is the ideal mechanical advantage of the ramp?
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A construction worker moves a crowbar through a distance of 0.50m to lift a load 0.05m off of the ground. What is the IMA of the crowbar?
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The IMA of a simple machine is 2.5. If the output distance of the machine is 1.0m, what is the input distance?
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You have just designed a machine that uses 1000J of work from a motor for every 800J of useful work the machine supplies. What is the efficiency of your machine?
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If a machine has an efficiency of 40%, and you do 1000J of work on the machine, what will be the work output of the machine?
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Lever
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Wheel and Axle
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Pulley
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Inclined Plane
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Screw
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Wedge
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Work Work In = Work Out Work = Force Distance
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Do DI FoFI
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Wout = WinFo x Do = FI x DI
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Example: If the stone has to be moved to 0.1m high, how far does Mr. Clune have to apply his force.Given: Fo = 1000N Find: de = ? dr = 0.1m Fe = 10NEquation: de = ( Fr x dr ) / Fe = ( 1000N x 0.1m ) / 10Nde = 10m
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Ideal Mechanical Advantage IMAIdeal Machine A machine in which the work input equals work output.Win = Wout
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The Lever Fulcrum..FoFiDoDiA bar that is free to pivot about a fixed point..
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IMAlever = input arm length output arm lengthIMA for the Lever
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Example: A screwdriver is used to pry open the lid of a paint can. The output arm is 0.50cm long. The input arm is 20cm long. What is the mechanical advantage of the screwdriver?Given: Do = 0.50cm Find: IMA Di = 20cmEquation: MA = DiDoSolve:IMA = 20 cm 0.50cm IMA = 40
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Classes of LeversFirst Class Second Class Third Class
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Wheel and AxleA wheel and axle is a simple machine consisting of two wheels of different sizes that rotate together.
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Wheel and Axle
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No Power Steering!!
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Wheel and Axle
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IMA of a Wheel and Axlerw ra IMA = radius of wheel radius of axle
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Example: An antique car, with no power steering, has a steering wheel with a radius of 20cm. The wheel turns an axle that has a radius of 2cm. What is the Mechanical Advantage of this wheel and axle system?Given: rw = 20cm Find: IMA = ? ra = 2cmEquation: IMA = rw raSolve: IMA = 20cm 2cmIMA = 10
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Inclined PlaneA slanted surface used to raise objects
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IMA of an Inclined Planelh
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Example: A piano must be raised from the ground to the first floor, a distance of 0.5m. A 10m plank is used to help to movers pick the piano up. If the piano weighs 3000N, what force do the movers have to apply to the piano?
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Fo = 3000Nl = 10mh = .5m
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Given: length ( l ) = 10m height ( h ) = 0.5m Fo = 3000NFind: IMA = ?Fi = ?
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Equation: IMA = l hSolve IMA = 10m 0.5m Equation: Fi = Fo MA Solve Fi = 3000N 20Fi = 150NIMA = 20
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WedgeAn inclined plane with either one or two sloping sides.MoreIMA
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ScrewAn inclined plane wound around a cylinder.IMAScrew Number of ThreadsMoreIMA
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PulleysFixed Pulley Movable Pulley
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Fixed Pulleys
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Fixed PulleysFixed Pulley OI
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Movable Pulleys
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Movable PulleysMovable Pulley OI
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Ideal Mechanical Advantage of a Pulley: The number of ropes segments supporting the resistance weight. IMA = 1 30N30N 30N
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Ideal Mechanical Advantage of a Pulley: The number of ropes segments supporting the resistance weight. IMA = 2 30N 15N 15N 15N
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Ideal Mechanical Advantage of a Pulley: The number of ropes segments supporting the resistance weight. IMA = 3 30N 10N 10N 10N 10N
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Block and Tackle The arrangement of several pulleys.
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Compound Machine A machine made by combining two or more simple machines together.
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Packet 14-4 Word Wise & Math Due: 4/13/10Homework 14-4Test: 4/15/10
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Mending with MachinesBionicsThe science of designing artificial replacements for parts of the human body
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ProsthesesArtificial replacements for human limbs.
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Functional Neuromuscular StimulationFNSBrain
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Section Wrap-Up Page: 197Due 01/7/05Homework 7-4
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PowerPower is the rate at which work is done.
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Example : A figure skater lifts his partner, who weighs 450N, 1.0m in 3.0s. How much power is required.d = 1mt = 3s
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Given: F = 450N d = 1.0m t = 3.0sFind: PowerP = 150W
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