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Simple Machines. -a machine that does work with one movement. 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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Simple Machines -a machine that does work with one movement
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
First class lever • Fulcrum is located between the input force and the output force • screwdriver opening paint can • HW: 5 1st class levers
Second class lever • Ouput force is located between the input force and the fulcrum • Wheel barrow Output force fulcrum Input force
Third class lever • Input force is located between the output force and the fulcrum • Baseball bat, rake, hockey stick fulcrum Output arm Input arm
Mechanical advantage of lever • MA = length of input arm = Li length of output arm Lo
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?
Pulleys • Grooved wheel with a rope, chain, or cable running through the groove • Fixed pulleys • Change direction of force • Gravity Help! • MA = 1
Movable Pulleys • Move when a force is applied. • MA = 2 • Multiply the input force 2x.
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.
Wheel and Axle • Two wheels of different sizes that rotate together • Can you think of any? • Doorknobs • Faucets • Steering wheel • Stereo volume knobs
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
Mechanical advantage of W&A • MA = radius of wheelrw radius of axle ra
Inclined Planes • A sloping surface that reduces the amount of force needed to do work • Ramps • Roads
Mechanical advantage of IP • MA = length of slope l height of slope h h l
Screw • Inclined plane wrapped around a cylindrical post • Wood screws • Soda lids • Olive jars
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
Compound Machines • Two or more simple machines working together to perform a task • Scissors • Faucets • Jeeps
The End Calculations are next!
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
MA of levers • MA = length of input arm length of output arm = 15 m 3 m = 5
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.
MA of W&A = radius of wheel radius of axle = 12 cm 1.2 cm = 10
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.
MA of I.P. = length of ramp height of ramp 8 m MA = 8 m 2 m = 4 2 m
MA of pulleys! 120 N 120 N 120 N 120 N