Simple Machines

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Simple Machines
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What is a Simple Machine?

• A simple machine is a device that helps to
  accomplish a task by redirecting or alleviating
  some of the work input required.
• Simple machines cannot create energy. They can
  only redistribute or produce force on an object.
• The six basic simple machines are the lever, the
  inclined plane, the wedge, the screw, the wheel,
  and the pulley.
• Simple machines help people lift or move heavy
  objects, split thick solids, and secure things
  together.

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Levers

• Lever a long piece of wood, metal, etc. that
  rests on a turning point (fulcrum) to lift or
  open something
• An object (load) is placed on one end, while a
  force pushes the other end down to move the
  object.
• Force applied x Distance (between force and
  fulcrum) Load x Distance (between load and
  fulcrum)
• Examples bottle openers, scissors, hammers (when
  pulling a nail out)

Applied force ?
? Lesser force (load)
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Lever Types

• First Class Lever
• Fulcrum is between force input and load.
• Input (effort) and load forces are on opposite
  sides, but act in the same direction.
• The closer the fulcrum is to the load, the less
  effort is needed.
• Examples see-saws, pliers, scissors
• Second Class Lever
• Load is between force and fulcrum.
• Effort and load forces are on the same side of
  the fulcrum but act in opposite directions.
• The closer the load is to the fulcrum, the less
  effort is needed.
• Examples staplers, nutcrackers

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More Lever Types

• Third Class Lever
• Force is between fulcrum and load.
• Effort and load forces are on the same side, but
  act in opposite directions.
• Effort required to lift the load is greater than
  the load.
• Examples fishing rods, tongs, brooms
• For first and second class levers large output
  of force is gained over a small distance (force
  multiplier)
• For third class levers small output of force is
  gained over a large distance (speed or distance
  multiplier)

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Pulleys

• A pulley is a wheel and axle over which a rope or
  chain is pulled in order to lift or lower heavy
  objects.
• Pulleys change the direction of motion/force
  applied to lift an object.
• The amount of force required to move the object
  remains the same
• Using a pulley feels easier because you are
  working with gravity by pulling down on the rope,
  as opposed to working against it by pulling the
  object straight up.

lt Without the use of a pulley, the required
lifting force is 100lbs.
With the use of a pulley, the required lifting
force is still 100lbs. gt
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Multiple Pulleys

• Force required when using more than one pulley to
  pull up an object is less than force required
  when using one pulley to pull up the same object.
  
• This is because the weight of an object is split
  by the number of pulleys you use.
• However, the distance of the rope multiplies by
  the number of pulleys you use also.

Two pulleys force required is cut in half, rope
length is increased.
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Inclined Planes

• An inclined plane is a surface set at an angle
  against the horizontal.
• Inclined planes split gravitational force in two
  
• Force parallel to plane
• Force perpendicular to plane
• Only parallel force must be counteracted when
  moving objects up a plane
• Force required to do work is less than when
  pushing on a flat surface
• Mechanical advantage slope/length of plane
• Used as ramps or sloping roads, and can be
  combined to form a wedge

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Wedges

• Wedges consist of a pair of inclined planes set
  against each other.
• By moving the planes relative to each other, a
  wedge builds up force in a direction
  perpendicular to the moving wedge.
• Mechanical advantage slope/thickness The
  advantage gained requires corresponding increase
  in distance
• Wedges are used to separate or hold objects.
• Door stops, axes, and teeth are examples of
  commonly used wedges.

Wedge used to hold a door
Wedge used to separate an object
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Wheel and Axle

• A wheel and axle is a simple machine made up of
  two circular objects of different sizes rotating
  on the same axis.
• The wheel has the larger diameter, and turns
  about the smaller axle.
• Because a wheel is basically a lever that can
  turn 360o, effort or resistance force can be
  applied anywhere on that surface. The central
  point of the wheel and axle serves as the
  fulcrum.
• A force applied to the wheel is multiplied when
  it is transferred to the axle, which travels a
  shorter distance than the wheel.
• Since the wheel is larger than the axle, it
  always moves through a greater distance than the
  axle.

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Use of the wheel and axle

• The mechanical advantage (the number of times a
  machine multiplies the effort force) depends on
  the radius of the wheel and of the axle.
• The wheel allows objects to roll along the
  ground, decreasing surface friction by
  substituting rolling friction for sliding
  friction.
• The wheel can also be used to lift objects by
  wrapping a cord attached to a weight to the axle.
  It is less efficient than the lever at lifting
  objects.
• Examples screwdrivers, doorknobs, windmills,
  gears, Ferris wheels

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Screws

• A screw is another type of an inclined plane. It
  is a helical inclined plane wrapped around a
  cylinder to form a spiral, with a wedge at its
  tip.
• The main use of a screw is to hold objects
  together with its helical grooves.
• A screw can convert a rotational force to a
  linear force and linear force to rotational force.

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Use of Screws

• The screws ratio of threading determines its
  mechanical advantage.
• Screws with wide grooves are harder to turn, yet
  travel a shorter distance to their destination.
• Screws with narrow grooves are easy to turn, but
  have to be twisted over a greater spiral
  distance.
• One example of the screw as a simple machine is
  Archimedes Screw - used to bring water up from
  low sources to the location of use by passing
  through a helix.
• Other examples of screws include bottle caps,
  worm gears, drills, wrenches, jacks, and light
  bulbs.

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Simple and Compound Machines

• A compound machine is composed of multiple simple
  machines working together to redirect or apply
  force.
• While a simple machine has only one motion,
  complex machines may have two or more.
• Examples of compound machines are a wheelbarrow,
  which uses a lever and a wheel and axle to
  redirect pushing force, and a bicycle, which
  redirects force from the users feet through
  pulleys to turn the wheels and propel the user
  forward.

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Works Cited

• http//www.uark.edu/depts/aeedhp/agscience/simpmac
  h.htm
• http//www.enchantedlearning.com/physics/machines/
  Levers.shtml
• http//www.simplemachines.info/netscape.htm
• http//www.howstuffworks.com/pulley.htm?printable
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• http//www.sciencebyjones.com/simple_machines.htm
• http//www.usoe.k12.ut.us/curr/science/sciber00/8t
  h/machines/sciber/intro.htm
• http//www.mos.org/sln/Leonardo/InventorsToolbox.h
  tml