Simple Machines

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Simple Machines
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What is a Simple Machine?

• A simple machine has few or no moving parts.
• Simple machines make work easier

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Wheels and Axles

• The wheel and axle are a simple machine
• Gears are a form of wheels and axles

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Pulleys

• Pulley are wheels and axles with a groove around
  the outside
• A pulley needs a rope, chain or belt around the
  groove to make it do work

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Inclined Planes

• An inclined plane is a flat surface that is
  higher on one end
• Inclined planes make the work of moving things
  easier

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Wedges

• Two inclined planes joined back to back.
• Wedges are used to split things.

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Screws

• A screw is an inclined plane wrapped around a
  shaft or cylinder.
• The inclined plane allows the screw to move
  itself when rotated.

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Levers-First Class

• In a first class lever the fulcrum is in the
  middle and the load and effort is on either side
• Think of a see-saw

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Levers-Second Class

• In a second class lever the fulcrum is at the
  end, with the load in the middle
• Think of a wheelbarrow

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Levers-Third Class

• In a third class lever the fulcrum is again at
  the end, but the effort is in the middle
• Think of a pair of tweezers

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Simple Machines

• Simple Machines can be put together in different
  ways to make complex machinery

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Simple Machines- Mechanical Advantage

• Mechanical advantage (MA) is the ratio of the
  force put into the machine (Effort Force) to the
  force the machine exerts on an object (Resistance
  Force).
• MA Fr / Fe
• MA gt 1 means that the machine makes work easier
  and increases the amount of force applied

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A sample problem

• A worker uses a pulley to lift a 45 kg object.
  If the mechanical advantage of the pulley is 5.2,
  what is the effort force exerted by the worker?

MA Fr / Fe
5.2 441 N / Fe
Effort Force ??? Mass 45 kg Resistance Force
45 9.8 441 N
Effort Force 85 N
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A sample problem You try it

• A worker uses a lever to lift an object with a
  mass of 3500 N. If the force applied by the
  operate was 1500 N, what is the mechanical
  advantage of the lever?

MA Fr / Fe
MA 3500 N / 1500 N
Effort Force 1500 N Resistance Force 3500 N
MA 2.33
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Simple Machines Ideal Mechanical Advantage

• Ideal Mechanical advantage is the ratio of
  distance moved by the person (de ) to the
  distance the machine moved the object (dr ).
• IMA de / dr
• LOOK AT PAGE 266 Figure 10-9

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A Sample Problem- You Try it

• A worker testing a multiple pulley system to
  estimate the heaviest object the system could
  move. When the worker moves the rope 1.5 m, the
  object moves 0.25 m. What is the IMA of the
  system?

IMA de / dr
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Simple Machines - efficiency

• Efficiency is the ratio of work output (Wo) to
  work input (Wi ) multiplied by 100.
• Efficiency e (Wo / Wi ) 100
• Another way to calculate it using mechanical and
  ideal mechanical advantage
• Efficiency e (MA / IMA) 100

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A sample problem

• A man exerts a force of 310 N on a lever to raise
  a crate with a mass of 910 kg. If the
  efficiency of the lever is 78, what is the
  levers IMA?

e (MA / IMA) 100
IMA de / dr
MA Fr / Fe
Effort Force 310 N Mass 910 kg Resistance
Force 910 9.8 8910 N
e (MA / IMA) 100 78 (28.7 / IMA) 100 IMA
36.8
MA 8910 / 310 MA 28.7
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A sample problem You Try It

• A man exerts a force of 650 N on a lever to raise
  a crate with a weight of 1000 N. If the
  efficiency of the lever is 55, what is the
  levers IMA?

e (MA / IMA) 100
IMA de / dr
MA Fr / Fe
Effort Force 650 N Resistance Force 1000 N
e (MA / IMA) 100 55 (1.53 / IMA) 100 IMA
2.8
MA 1000 / 650 MA 1.53
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Homework

• Page 280
• Problems 79-84