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Advanced Physical Science Ms. Pollock 2010 - 2011
Machines Advanced Physical Science Ms. Pollock
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What is a machine? Machine – device that makes doing work easier
Does not have to be complex Can increase force applied to object Can increase distance over which force is applied
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What is a machine?
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Input and Output Force Two forces involved when machines used to do work Input force – force applied to machine Output force – force applied by machine Machines MUST conserve energy. It cannot be gained or lost. Output work will always be less than input work.
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Input and Output Forces
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Ideal Machines If there were no friction, no energy would be converted to heat. Work input would equal work output. Ideal machines can “increase” the amount of force that is output.
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Mechanical Advantage Ratio of output force to input force MA = Fout
Fin Ideal mechanical advantage ignores friction
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Efficiency How much work put into a machine is changed into useful output work Efficiency = Wout X 100 % Win Lubricant added to reduce friction and increase efficiency
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Simple Machines Machine that does work in only one movement Six types
Lever Pulley Wheel and Axle Inclined Plane Screw Wedge
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Simple Machines
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Levers Bar that is free to pivot around a fixed point
Fixed point – fulcrum Output force dependent of lengths of input arm and output arm Three classes of levers
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Levers
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Levers First Class Second Class Third Class
Fulcrum between input and output forces Screwdriver opening paint can Second Class Output force located between fulcrum and input force wheelbarrow Third Class Input force between output force and fulcrum Bat hitting ball
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Levers
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IMA of a Lever IMA = length of input arm length of output arm
IMA = Lin Lout
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Pulleys Grooved wheel with rope, chain, or cable running along groove
Two types Fixed Changes only direction of force Movable Reduces force needed to move object
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Pulleys
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Fixed Pulleys Attached to something that does not move IMA = 1
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Movable Pulleys End of rope fixed, wheel free to move
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Block and Tackle System of fixed and moveable pulleys
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Wheel and Axle Shaft or axle attached to center of larger wheel
Rotate together IMA= radius of wheel radius of axle Gear – wheel and axle with teeth around outside edges
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Wheel and Axle
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Inclined Planes A sloping surface that reduces the amount of force required to do work IMA = length height Spreads force out over greater distance
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Inclined Plane
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The Screw Inclined plane wrapped in spiral around cylindrical post
Modified inclined plane
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The Wedge Inclined plane that moves through an object or material
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Compound Machines Two or more simple machines that operate together
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Challenge List EVERY simple machine you can think of that you have PERSONALLY USED today. The person with the most LEGITIMATE answers wins.
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