Transcript Simple Machines

Bell Ringer 3-3-10
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Why do we use machines?
What is the formula for work?
What are the SI units for work?
What is the formula for power?
What are the SI units for power?
Simple Machines
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Simple machines do work with only one movement.
A machine made of a combination of simple machines and
makes more than one movement is a compound machine.
1. Inclined plane
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A flat, sloped surface.
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Less force is needed to move an object from one height to
another using an inclined plane than is needed to lift the object.
The mechanical advantage of an incline is the length of the
inclined plane divided by its height.
 Ex: Ramp
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2. Wedge
An inclined plane that moves
 It changes the direction of the applied force.
 A wedge is really an inclined plane turned on its side. But
instead of helping you move things to a higher level, a wedge
helps you push things apart.
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Ex: blades of a knife, axe, door stop, or a shovel
 MA = length
width
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A wedge can also be round, like the tip of a nail, or the tines on your fork.
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Basically, the wedge works just like a ramp: The narrower the wedge (or the
sharper the point of a wedge), the easier it is drive it in and push things apart.
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But here's the trade-off: To split something apart really wide, you have to push
the wedge a long distance.
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We can use the wedge action to cut and shape ice and wood sculptures.
3. Screw
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An inclined plane wrapped around a cylinder or post.
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The inclined plane forms the screw threads (spiral) on a screw.
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A screw is a simple machine that is made from another simple
machine. It is actually an inclined plane that winds around
itself.
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A screw has ridges and is not smooth like a nail. Some screws are used to
lower and raise things. They are also used to hold objects together.
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Ex: screws, jar lids
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The mechanical advantage of the screw is the length of the inclined plane
wrapped around the screw divided by the length of the screw.
Video
Inclined Plane, Screw, Wedge
 Quiz After!!
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Bell Ringer 3-4-10
Solve the following problems. Include units and show your
work!!
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A force of 15 newtons is used to push a box along the
floor a distance of 3 meters. How much work is done?
A book that weighs 1 N is lifted 2 meters. How much
work is done?
It took 50 joules to push a chair 5 meters across the floor.
With what force was the chair pushed?
4. Lever
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Any rigid rod or plank that pivots about a point.
The point about which the lever pivots is called a fulcrum.
Levers can be divided into 3 classes depending on the position of the
fulcrum.
The mechanical advantage is dividing the distance from the fulcrum
to the input force by the distance from the fulcrum to the output
force.
5. Wheel and Axle
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Two circular objects of different sizes that rotate together.
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A wheel and axle is a lever that rotates in a circle around a
center point or fulcrum.
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The larger wheel (or outside) rotates around the smaller wheel
(axle).
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Bicycle wheels, ferris wheels and gears are all examples of a
wheel and axle.
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Wheels can also have a solid shaft with the center core as
the axle such as a screwdriver or drill bit or the log in a log
rolling contest.
6. Pulley
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The pulley is a simple machine made of a wheel with a rope or belt
wrapped around it. It is used to lift things up.
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When you pull down on one end of the rope, the other end moves
upward. A pulley can help move an object to a place that is hard to
reach. .
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Fixed pulleys such as on window blinds or flagpoles, are attached to an
overhead structure and change the direction of the force you exert.
Exit Quiz
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What is the name for a flat, sloped, surface?
What is the simple machine that is involved in a
flagpole?
Tell me an example of a lever in the real world.
Why do we use machines?