simple machines
DESCRIPTION
TRANSCRIPT
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SIMPLE MACHINE
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\\Sv0002\stares$\Middle School\Science\Gr. 8\2006-2007\Quarter 4\Simple Machines\Videos (1)
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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 dWork = 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
EFFORTFORCE
DISTANCE
OUTPUTFORCE
DISTANCE
Multiply the force
Multiply the distance
Change in Direction
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TYPES OF WORKA.INPU
T 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
EFFORTFORCE
DISTANCE
OUTPUTFORCE
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 forcex 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 LeversAn 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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SCREWSA screw is a cylinder with an
inclined plane wrapped around it.
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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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