simple machines -a machine that does work with one movement
TRANSCRIPT
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Simple Machines-a machine that does work with one movement
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Levers A bar that is free to pivot, or turn,
about a fixed point Fulcrum- fixed point on the lever Input arm- part of lever that person
adds input force to Output arm- part of lever that moves
the output force or work
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3 types of Levers
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First class lever Fulcrum is located between the input force and
the output force screwdriver opening paint can HW: 5 1st class levers
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Second class lever Ouput force is located between the
input force and the fulcrum Wheel barrow
fulcrum
Input force
Output force
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Third class lever Input force is located between the
output force and the fulcrum Baseball bat, rake, hockey stick
fulcrum
Input arm
Output arm
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Mechanical advantage of lever
MA = length of input arm = Li
length of output arm Lo
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Homework Calculate the MA of a wheel barrow
that has 5 feet from the wheel to handle. The center of the load is exactly 2.5 feet from the wheel.
What would you do to design a better wheel barrow?
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Pulleys Grooved wheel with a rope, chain,
or cable running through the groove
Fixed pulleys Change direction of force Gravity Help! MA = 1
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Move when a force is applied. MA = 2 Multiply the input force 2x.
Movable Pulleys
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Pulley SystemsBlock and Tackle
A system of fixed and movable pulleys
MA = number of ropes supporting the weight
Do not count rope that you pull down on.
Do count a rope that you pull up on.
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Wheel and Axle Two wheels of different sizes that
rotate together Can you think of any?
Doorknobs Faucets Steering wheel Stereo volume knobs
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Gears Form of wheel and axle Two wheels of different sizes with
interlocking teeth Multiply the input force, input
distance, and change direction of force
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Mechanical advantage of W&A
MA = radius of wheel rw
radius of axle ra
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Inclined Planes A sloping surface that reduces the
amount of force needed to do work Ramps Roads
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Mechanical advantage of IP MA = length of slope l height of slope h
h
l
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Screw Inclined plane wrapped around a
cylindrical post Wood screws Soda lids Olive jars
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Wedge Inclined plane with one or two
sloping sides that moves through an object or material to change the direction of the force. Knives Axes
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Compound Machines Two or more simple machines
working together to perform a task Scissors Faucets Jeeps
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The End
Calculations are next!
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Calculations Calculate the Mechanical
Advantage of a lever that has an input arm of 15 meters and a output arm of 3 meters.
15 m
3 m
fulcrum
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MA of levers MA = length of input arm length of output arm
= 15 m 3 m
= 5
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MA of a Wheel and axle Calculate the MA of the door knob
that you turn as you try to sneak into Mr. Miller’s room tardy.
The knob itself has a radius of 12 cm and the axle that runs through the knob as a radius of 1.2 cm.
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MA of W&A = radius of wheel radius of axle
= 12 cm 1.2 cm
= 10
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MA of an Inclined Plane Calculate the mechanical
advantage of an inclined plane/ramp used to load your ATV onto the bed of a truck.
The truck’s bed is exactly 2 meters off the ground and the ramp is 8 meters long.
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MA of I.P. = length of ramp height of ramp
MA = 8 m 2 m = 4
2 m
8 m
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MA of pulleys!
120 N
120 N
120 N
120 N