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SIMPLE MACHINES http://www.flixxy.com/best-rube-goldberg-machine.htm \\Sv0002\stares$\Middle School\Science\Gr. 8\2006-2007\Quarter 4\Simple Machines\Videos (1) Video Clips:

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MACHINES Work is …………………….…… What is a machine?........ Why use machines?.........

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WORK is the transfer of energy from one physical distance to another Measured in Joules W = F x d Work = Force x Distance

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MACHINES …..any device or instrument that helps you do something

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machines make work we do easier

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WORK = FORCE x DISTANCE WORK INPUT WORK OUTPUT INPUT = OUTPUT EFFORT FORCE DISTANCE OUTPUT FORCE DISTANCE Multiply the force Multiply the distance Change in Direction

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TYPES OF WORK A.INPUT work that goes into the machine needs effort force

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B. OUTPUT Work done by the machine Resistance Force

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Machines do not increase work output “Work output is never greater than work input”

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WORK = FORCE x DISTANCE WORK INPUT WORK OUTPUT INPUT = OUTPUT EFFORT FORCE DISTANCE OUTPUT FORCE DISTANCE Multiply the force Multiply the distance Change in Direction

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Work in = Work out Work input (force to move something over a distance) Work output (force from the machine to move something over a distance) Machines make work easier because they change either the _________ or _________of the force put into the machine.

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What is Mechanical Advantage? Number of times a machine multiplies the effort force Tells how much force is gained by using machine

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Mechanical Advantage = Output Force Input Force Examples: Inclined Plane: M.A. = Load Effort = 5N/0.2N = 25 Pulley: M.A. = Load Effort = 6.5N/1.5N = 4

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so … …. Half the force needed = MA of 2 One third the force = MA of 3 A MA of less than 1 = increase force, but over a smaller distance (faster but harder)

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Output force Input force x 100% Efficiency of the machine = Expressed as a percentage EFFICIENCY

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LEVERS Simple machines used to lift weights

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First Class Levers An example of this type is a seesaw.

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Second Class Lever The difference from the first class lever is that the fulcrum is on the end, instead of in the middle.

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Third Class Lever The load is the fish; the handle end is the fulcrum.

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The force you exert on the machine is called the input force or the effort force. The force exerted by the machine is called the output force or the resistance force. If you compare the input force to the output force, you can determine the advantage of using a machine. A machine’s mechanical advantage is the number of times a force exerted on a machine is multiplied by the machine. 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.

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Pulley Changes the direction of the force and the amount of force. Lever Increase input force and direction (eg prying open a can of paint)

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INCLINED PLANE

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Inclined Plane -A simple machine that makes it easier to move a heavy object to a higher or lower elevation. -It reduces the amount of force needed to lift the object by increasing the distance.

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INCLINED PLANE Increases the distance so reduces the force Ideal MA = Length Height

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The Egyptians used inclined planes to build the pyramids.

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WEDGES - A wedge is a simple machine shaped like an inclined plane. - It is like a portable inclined plane.

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SCREWS A screw is a cylinder with an inclined plane wrapped around it. inclined plane

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Wedge and Screw Force is applied over a longer distance Think of the screw being a long inclined plane!!!

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WHEEL AND AXLE - made up of two circular objects of different sizes Smaller Object (axle) Larger Object (wheel)

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Wheel and Axle Wheel = Large diameter Axle = Small diameter This is a Force Multiplier – over a longer distance

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