What is a Machine Ch 8.2 8th

8/14/2019 What is a Machine Ch 8.2 8th

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Chapter 8 Section 2


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Objectives:Explain how a machine makes work easier.

Describe and give examples of the force-distancetrade-off that occurs when a machine is used.

Calculate mechanical advantage.

Explain why machines are not 100% efficient.


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Machines: Making Work

EasierVocabulary:Machine: a device that makes work easier by

changing the size or direction of a forceWork input:the work you do on a machineThe product of the input force and the distance

through which the force is exerted

Work output:The work done by a machineThe product of the output force and the distance

through which the force is exerted


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Input & Output forces:

http://www.affordablehousinginstitute.org/blogs/us/seesaw_leverage_small.jpg

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3/sx6087b3.gif


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Same work, different

force:Machines make work easier by changing the

size or direction of the input force

Machines help to decrease the input force andincrease the distance over which the force is

exerted


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Mechanical

Advantage:Vocabulary:

Mechanical advantage: a number that tells how manytimes a machine multiplies force

Formula:Mechanical advantage (MA) = output force input force

Ex: Push 500N weight up a ramp using 50N of force

MA = 500N 50N = 10

MA > 1 helps to move or lift heavy objects

MA < 1 reduces output force, but the distance an objectmoves


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Mechanical

Efficiency:Vocabulary:

Mechanical efficiency: a comparison of a

machines work output with the work inputFormula:

Mechanical efficiency = work output workinput x 100

The work outputof a machine can never begreater than the work input

Friction


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Perfect Efficiency??An ideal machine = 100% efficiency (usually

not possible)

New technologies are being used to increaseefficiencyEx: train floating on magnets (page 221, fig. 6)

Ex: using lubricants (oil, grease) to decreasefriction to increase efficiency)


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Quick Quiz:How does a machine make work easier?

What two things do you need to know in orderto calculate mechanical efficiency?

If the mechanical advantage of a machine is

5, how does the output force compare withthe input force?

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What is a Machine Ch 8.2 8th