5-2 Mechanical Advantage And Efficiency

Mechanical Advantage and Efficiency Chapter 5 Section 2 Page 160

What is a Machine? • Machine- a device with which you can do work in a way that is easier or more effective • A machine makes work easier by changing the amount of force you exert, the distance over which you exert your force, or the direction in which you exert your force • Input force- force you exert on the machine that does work (effort force) • Output force- force exerted by the machine (resistance force)

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Multiplying Force

• Work= force x distance • If work stays the same, decrease in force must mean an increase in distance • You do as much work with the machine as you would without the machine

Multiplying Distance

Changing Direction

• Some machines, input force is greater than output force • Hitting a hockey puck • Waving a paper fan

S o m e m a ch in e s d on ’t m u ltip ly e ith e r fo rce o r d ista n ce R a isin g a sa il Pu lle y 

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M e ch a n ica l Mechanical Mechanical Advantage A d v a n ta g e o f Advantage of

Mechanical Advantage of Multiplying Force 

• A machine’s mechanical advantage is the number of times a force exerted on a machine is multiplied by the machine (ratio of output force to input force) • Mechanical advantage= output force/input force

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C h a n g in g D ire ctio n

If only the direction of a force changes, the input force will be the same as the output force. M.A. = 1

Multiplying Distance

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For a machine that multiplies distance, the output force is less than the input force Mechanical Advantage less than 1 Input of 20N, output of 10 N, M.A. = .5N

Mechanical Advantage

Efficiency of Machines Efficiency

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The less friction there is, the closer the output work is to the input work. • Efficiency of a machine compares the output work to the input work • Efficiency is expressed as a % • •

Calculating Efficiency

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• To calculate efficiency of a machine, divide the output work by the input work and multiply the result by 100% • Efficiency = output work / input work x 100% • Actual mechanic advantagethe mechanical advantage that a machine provides in a real situation • Ideal mechanical advantagemechanical advantage of a machine without friction • The more efficient a machine, the closer it is actual mechanical

Efficiency Problem • You cut the lawn with a hand lawn mower. You do 250,000 J of work to move the mower. If the work done by the mower in cutting the lawn is 200,000 J, what is the efficiency of Efficiency = .8 x 100% the mower? = 80% Output Work • Efficiency = ----------------- X 100% Input Work

Efficiency =

200,000 N ----------------250,000 N

X

100%