Chapter 14Work, Power and Machines

dFChapter 14.1

WorkWork Requires Motion The force must act in the same direction that the object moves. If there is no movement, no work is done.

Work depends on direction!!

Work depends on direction!!No Work!!

Work depends on direction!!

WorkWork = Force X distanceW = F X dW = Newton X meter = NmW = Joule (J)

WFdW =FdF =d =

PowerPower =

WPtW =PtP =t =

Increase PowerIncrease work done in same time.

Same amount of work in less time.

PowerPower =P == Watts= W

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?

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

James Watt - Horsepower1 horsepower is equal to 746 watts

HomeworkWorksheet: 14-1Due: 4/5/10

MachinesCan machines decrease work???Work = Force X distanceChapter 14.2

Machines do Work

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

Increasing Force

Direction of Force

Distance the force acts.

Work Input and Work Output

Work Input and Work Output

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).

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

Work Input to a machine

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.

Work Output from a machine

HomeworkWorksheet: 14-2Due: 4/5/10Worksheet: 14-1

Chapter: 14-3Mechanical Advantage AndEfficiency

ActualMechanical AdvantageActual Mechanical Advantage (MA) The number of times a machine multiplies the Input Force.

ActualMechanical Advantage FO FI

Output Force - FO Input Force - FI

ActualMechanical AdvantageMA = Output Force Input force MA = FO FI

Experiment

IdealMechanical Advantage(IMA) IMA of a machine is the mechanical advantage in the absence of friction.

IdealMechanical Advantage

Ideal Mechanical Advantage - IMAIMA = Input Distance Output Distance MA = DI DO

Experiment

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?

Given: MA = 100 Fr = 1000NEquation: Fe = Fr MASolve: Fe = 1000N 100Fe = 10N Find: Fe = ?

EfficiencyThe measure of how much work put into a machine is changed to useful work put out by the machineWorkInput(WIN)WorkOutput(WOUT)

WOUT WINEfficiency = X 100%

Experiment

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

l = 4m(DI)h = 1m (Do)

Given: Fo = 1500N Do = 1.0m FI = 500N DI = 4.0mFind: Efficiency = ?Efficiency = 75%

HomeworkWorksheet: 14-3Math Practice:Page: 425 1-3Page: 426 8-9Due: 4/7/10

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?

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?

The IMA of a simple machine is 2.5. If the output distance of the machine is 1.0m, what is the input distance?

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?

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?

Lever

Wheel and Axle

Pulley

Inclined Plane

Screw

Wedge

Work Work In = Work Out Work = Force Distance

Do DI FoFI

Wout = WinFo x Do = FI x DI

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

Ideal Mechanical Advantage IMAIdeal Machine A machine in which the work input equals work output.Win = Wout

The Lever Fulcrum..FoFiDoDiA bar that is free to pivot about a fixed point..

IMAlever = input arm length output arm lengthIMA for the Lever

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

Classes of LeversFirst Class Second Class Third Class

Wheel and AxleA wheel and axle is a simple machine consisting of two wheels of different sizes that rotate together.

Wheel and Axle

No Power Steering!!

Wheel and Axle

IMA of a Wheel and Axlerw ra IMA = radius of wheel radius of axle

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

Inclined PlaneA slanted surface used to raise objects

IMA of an Inclined Planelh

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?

Fo = 3000Nl = 10mh = .5m

Given: length ( l ) = 10m height ( h ) = 0.5m Fo = 3000NFind: IMA = ?Fi = ?

Equation: IMA = l hSolve IMA = 10m 0.5m Equation: Fi = Fo MA Solve Fi = 3000N 20Fi = 150NIMA = 20

WedgeAn inclined plane with either one or two sloping sides.MoreIMA

ScrewAn inclined plane wound around a cylinder.IMAScrew Number of ThreadsMoreIMA

PulleysFixed Pulley Movable Pulley

Fixed Pulleys

Fixed PulleysFixed Pulley OI

Movable Pulleys

Movable PulleysMovable Pulley OI

Ideal Mechanical Advantage of a Pulley: The number of ropes segments supporting the resistance weight. IMA = 1 30N30N 30N

Ideal Mechanical Advantage of a Pulley: The number of ropes segments supporting the resistance weight. IMA = 2 30N 15N 15N 15N

Ideal Mechanical Advantage of a Pulley: The number of ropes segments supporting the resistance weight. IMA = 3 30N 10N 10N 10N 10N

Block and Tackle The arrangement of several pulleys.

Compound Machine A machine made by combining two or more simple machines together.

Packet 14-4 Word Wise & Math Due: 4/13/10Homework 14-4Test: 4/15/10

Mending with MachinesBionicsThe science of designing artificial replacements for parts of the human body

ProsthesesArtificial replacements for human limbs.

Functional Neuromuscular StimulationFNSBrain

Section Wrap-Up Page: 197Due 01/7/05Homework 7-4

PowerPower is the rate at which work is done.

Example : A figure skater lifts his partner, who weighs 450N, 1.0m in 3.0s. How much power is required.d = 1mt = 3s

Given: F = 450N d = 1.0m t = 3.0sFind: PowerP = 150W

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