ms. wickersham. concepts o all mechanical devices that humans use are made from six basic building...
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![Page 1: Ms. Wickersham. Concepts o All mechanical devices that humans use are made from six basic building blocks called simple machines. o It's important to](https://reader036.vdocuments.site/reader036/viewer/2022062320/56649cc05503460f949875b0/html5/thumbnails/1.jpg)
Ms. Wickersham
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Concepts
o All mechanical devices that humans use are made from six basic building blocks called simple machines.
o It's important to note that when a simple machine is used the same amount of work is require. o A SM reduces the amount of effort needed to move
an object, but it results in moving it a greater distance to accomplish the same amount of work.
o All complex mechanisms are made from simple machines.
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Simple Machines
Simple Machines: A simple device that provides a mechanical advantage, such as a wheel & axle, lever, pulley, or inclined plane.
Compound Machines: A system of two or more simple machines (the game mouse trap is a great example).
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LEVER AND FULCRUM
PULLEY
WHEEL AND AXLE
INCLINED PLANE
WEDGE (Modification of Inclined plane)
SCREWS (Modification of Inclined plane)
THERE ARE SIX SIMPLE MACHINES
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Machines do work for us.What is Work?
In order for work to be done, two conditions must be met:
o a force must move an object some distance
o and the force and distance the object moves must also be in the same direction.
Therefore, if the object does not move, no work is being done.
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Formula for Work
In order to calculate work you need to have the measurement for Force and Distance.
W=F x D W = Force (Newtons) x distance (meters) W = Force (lbs) x distance (feet)
http://www.youtube.com/watch?v=pDK2p1QbPKQ
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How do machines help us do work?
Mechanical advantage (MA) is the factor by which a mechanism multiplies the force put into it, making work easier.
Machines provide us with MA in the followingways:o A machine can increase the force o A machine can change the direction o A machine can increase the speed
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LEVER AND FULCRUM
o A simple machine consisting of a rigid bar and a fulcrum (pivot point).
o There are three classes:o 1st classo 2nd classo 3rd classo http://www.youtube.com/watch?
v=Us2KfO_yrPA
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Three classes of Levers
o The class of lever is determined by what is located in the middle.
o Use this diagram to help you remember.
o 1st class - fulcrum (pivot point) is in the middleo 2nd class - resistance (load) is in the middle o 3rd class - effort (force) is in the middle
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FIRST CLASS LEVER
1st class-the fulcrum is between the effort and the Load.
The closer the load is to the fulcrum, the less effort needed to lift the load.
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SECOND CLASS LEVER
2nd class- the LOAD is between the effort and the fulcrum.
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THIRD CLASS LEVER
o These levers are used least often because their MA is less than 1.
o This means the force needed to use them is greater than the force they can move.
3rd class- the EFFORT is between the Load and the Fulcrum
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How to calculate MA for levers:
Can be calculated in two ways:
If you know the distanceMA = Effort Arm
Resistance Arm (distance between the fulcrum and the input force)
If you know the weightMA = Load/Resistance Effort
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PULLEY
o Pulley: A simple machine consisting essentially of a wheel with a grooved rim in which a pulled rope or chain can run to change the direction of the pull and thereby lift a load.
o http://www.youtube.com/watch?v=9T7tGosXM58
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Pulley Systems
There are three types of pulley systems:
1. A FIXED PULLEY
2. A MOVABLE PULLEY and
3. A COMBINATION PULLEY
To calculate MA, you count the # of wheels
or ropes, excluding the effort rope.
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FIXED PULLEY
A fixed pulley is “fixed” to something such as a ceiling, it cannot move.
Work: changes the direction of the force
A fixed pulley doesn't reduce the effort.
MA = 0
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MOVABLE PULLEYS
A movable pulley is “movable” either vertically or horizontally.
Work: changes the direction of the force
MA = A movable pulley provides a mechanical advantage of 1.
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COMBINATION PULLEY
A combined pulley is a combination of the fixed and movable, sometimes called a block and tackle.
Work: changes the direction of the force
MA = weight/# of pulleys
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WHEEL AND AXLE
Wheel and Axle: a simple machine consisting of two concentric wheels.
Work: Increases the speed and changes direction
MA = wheel diameter/axle dia.
http://www.youtube.com/watch?v=XlZYPFDjTJM
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INCLINED PLANE Inclined plane: A simple
machine used to raise or lower a load by rolling or sliding it instead of lifting it vertically.
Work: Increases the force
MA = Slope / height
http://www.youtube.com/watch?v=pG_kT565-XQ
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WEDGES
o A piece of material, such as metal or wood, thick at one edge and tapered to a thin edge at the other
o The wedge is an inclined plane.
o MA = side length/thickness
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o The screw is an incline plane that is wrapped around a central axis.
o The distance between the ridges is called the pitch (the distance advanced in a single turn).
o MA = dia. of screw/lead of screw
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Mechanical Advantage
http://www.youtube.com/watch?v=rvscbkd3AzU&playnext=1&list=PL4S_gOG2-Y-hmAZqrMBtD5bqFcP3rBmkp&feature=results_main