Types of Machines Ch 8.3 8th

8/14/2019 Types of Machines Ch 8.3 8th

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Chapter 8 Section 3


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Identify and give examples of the six types

of simple machines

Analyze the mechanical advantage

provided by each simple machine

Identify the simple machines that make upa compound machine


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Definition: a simple machine that has a bar

that pivots at a fixed point, called a fulcrum

Used to apply a force to a load

There are 3 classes of levers


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The fulcrum is between the input force and

the load

Always change the direction of the input

force

Used to increase force or to increasedistance


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Fulcrum in the middle: MA = 1

Fulcrum closer to the load: MA > 1 (output

force is increased, exerted over a shorter

distance)

Fulcrum is closer to the input force:MA < 1 (output force is < input force,

distance increases) pg. 222, fig. 1


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Load is between the fulcrum and the inputforce

Do not change the direction of the input force

Allow you to apply less force than the forceexerted by the load

Output force is < input force over a > distance


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MA > 1

The closer the load is to the fulcrum, the

more force is increased and the greater

the MA is.


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Input force is between the fulcrum and the

load

Do not change the direction of the input

force

Do not increase the input force

Output force is always < the input force


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MA < 1

The force is decreased

Increase the distance through which the

output force is exerted


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Vocabulary:

Pulleys: a simple machine that consists of

a wheel over which a rope, chain, or wire

passes

Ex: elevator, window blinds


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Fixed Pulleys

Moveable Pulleys

Block and Tackles


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The pulley is attached to something that

does not move

You pull on a rope to lift a load

Pulley changes the direction of the force

MA = 1


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Attached to the object being moved

Does not change a forces direction

Do increase force

Increase the distance over which the inputforce must be exerted

MA = 2


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http://learn.uci.edu/media/OC08/11004/OC0811004_L6Pulley5.gif


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Fixed pulley and moveable pulley are used

together

Mechanical advantage depends on the

number of rope segments

http://upload.wikimedia.org/wikipedia/commons/c/ca/Block_and_tackle_(PSF).png


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https://reader010.{domain}/reader010/html5/0626/5b31530481a67/5b31530cc47b5.jpg


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Vocabulary:

Wheel and Axle: a simple machine

consisting of two circular objects of

different sizes; the wheel is larger of thetwo.

Ex: doorknobs, steeringwheels, faucets

http://learn.uci.edu/media/OC08/11004/OC0811004_L6WheelAndAxle2.gif


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Formula: divide the radius of the wheel by

the radius of the axle

MA > 1

Ex: MA = 15 cm/3cm = 5

http://www.allmachines.net/photos/Wheel-axle.gif


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Vocabulary:

Inclined Plane: a simple machine that is a

straight, slanted surface, which facilitates

the raising of loads; a ramp

Smallerinput force is needed over a

greaterdistance


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Formula: length of inclined plane divided

by height

MA = L/H

Ex: 4.8m/1.2m = 4

http://www.teachengineering.org/collection/cub_/lessons/cub_images/cub_simp_machines_lesson02_figure6.jpg


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Vocabulary:

Wedge: a simple machine that is made up

of two inclined planes and that moves;

often used for cutting.

Ex: knife, doorstop, plow, ax head, chisel

http://www.nvsd44.bc.ca/sites/img/2/2-470-4308.gif


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The longer and thinner the wedge, the

greater its mechanical advantage

MA = dividing the length by its greatest

thickness

Ex: MA = 8cm/2cm = 4



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Vocabulary:

Screw: an inclined plane that is wrapped in

a spiral around a cylinder

A small force is applied over a long

distance

Often used a fasteners


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The longer the spiral on a screw is and

closer together the threads are, the greater

the MA

http://www.forteachersforstudents.com.au/EngQuest/images/SM_diagram12.jpg


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MA = input distance/output distance

MA = x diameter/pitch or

= 3.14 x diameter/pitch



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A machine designed by Archimedes to

transfer water from a low-lying body of

water into irrigation ditches

Designed in 3rd century BC

http://en.wikipedia.org/wiki/File:Archimedes-screw_one-screw-threads_with-ball_3D-view_animated_small.gif

http://en.wikipedia.org/wiki/File:Archimedes_screw.JPG
http://upload.wikimedia.org/wikipedia/commons/8/82/Archimedes_screw.JPGhttp://upload.wikimedia.org/wikipedia/commons/2/22/Archimedes-screw_one-screw-threads_with-ball_3D-view_animated_small.gif


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A machine made of more than one simple

machine

Ex: block and tackle (2 pulleys)

Ex: can opener(2nd class lever, wheel &

axle, wedge)


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ME is usually low because there are so

many moving parts

There is more friction to overcome

Friction can be lowered by using lubricants

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Types of Machines Ch 8.3 8th