Ch14 ConceptsCh14 ConceptsEfficiencyEfficiency

WorkWork PowerPower MachinesMachines

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Work is the product of force Work is the product of force and distanceand distance

For a force to do work on an object, some of the For a force to do work on an object, some of the force must act in the direction the object moves. force must act in the direction the object moves.

No movement=no work doneNo movement=no work donework=force X distancework=force X distanceSI unit of work is the Joule (J)SI unit of work is the Joule (J)SI unit for force is the newton (N)SI unit for force is the newton (N)SI unit for distance is the meter (m)SI unit for distance is the meter (m)

Power is the rate of doing work.Power is the rate of doing work.

Doing work at a faster rate requires more Doing work at a faster rate requires more power. To increase power, you can power. To increase power, you can increase the amount of work done, or you increase the amount of work done, or you can do a given amount of work in less can do a given amount of work in less time.time.Power= Work/TimePower= Work/TimeThe SI unit of power is the watt (W)The SI unit of power is the watt (W)The SI unit of time is the second (s)The SI unit of time is the second (s)1 Watt= 1 j/sec1 Watt= 1 j/sec

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What is a machine?What is a machine?

A machine is a device that changes a A machine is a device that changes a forceforceThey make work easier to do.They make work easier to do.They change the size of a force needed, They change the size of a force needed, the direction of a force, or the distance the direction of a force, or the distance over which a force actsover which a force acts

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EfficiencyEfficiency

The percentage of work input that The percentage of work input that becomes work output is the efficiency of a becomes work output is the efficiency of a machinemachineBecause there is always some friction, the Because there is always some friction, the efficiency of any machine is less than efficiency of any machine is less than 100%100%It is expressed as a percentageIt is expressed as a percentageEfficiency =work output/work input X 100%Efficiency =work output/work input X 100%

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Simple MachinesSimple Machines

Six different types:Six different types: LeverLever Wheel and axleWheel and axle Inclined planeInclined plane WedgeWedge ScrewScrew pulleypulley

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Mechanical DevicesMechanical DevicesMany are made of Many are made of combinations of two or combinations of two or more of the six different more of the six different types of simple types of simple machinesmachinesA A compound machinecompound machine is is a combination of two or a combination of two or more simple machines more simple machines that operate together. that operate together. Ex. Car, washing Ex. Car, washing machine, clocks, etc.machine, clocks, etc.

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