Simple Machines

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Simple Machines

• Six Types
• Inclined Plane
• Lever
• Wedge
• Screw
• Pulley
• Wheel and Axle

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Inclined Plane

• Ramp
• Would you rather scale the face of this mountain,
  or take the road?
• Which requires more work? more effort?

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Lever

• crowbar
• wheelbarrow

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Types of Levers
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Wedge

• Axe

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Screw

• inclined plane wrapped around a rod
• Application of force over much greater distance
  increases your ability to drive the screw through
  wood.
• Compare the distance through which you turn the
  screwdriver to the distance the screw moves into
  the wood.

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Pulley

• Useful in lifting heavy objects

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Wheel and Axle

• Wheel connected to rigid pole
• Effort applied to large wheel to turn smaller
  axle.
• doorknob
• wheel on car
• conveyer belt

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Wheel and Axle
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Simple Machines

• device for multiplying force
• may also change the direction of a force
• Compound machinecombination of several simple
  machines
• bicycle

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Simple Machines

• Do NOT create energy
• Energy cannot be created or destroyed
• A machine multiplies force at the expense of
  distance.
• lever
• branch cutters
• screwdriver

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Simple Machines

• Ignoring energy loss due to friction, the
  following is true
• Work input Work output
• (Fin x din) (Fout x dout)
• If the output force is greater than the input
  force, it is accomplished at the expense of
  distance.

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Example 1

• You push on a lever with a force of 50N. The
  lever handle moves down 0.3m. What was the work
  input?

Win Fin x din Win (50N)(0.3m) Win 15J
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Example 2

• If the nail in the previous problem were raised a
  distance of 0.02m, with how much force did the
  lever pull up on the nail?

Fout x dout 15J Fout 15J/dout Fout
15J/0.02m Fout 750N
Wout Win Wout 15J
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Example 2
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Example 3

• You use a lever to lift a boulder. The boulder
  has a weight of 5000N. You push down on the
  lever with a force of 250N and the lever moves
  down 1m.
• In the process of lifting the boulder, what
  happens to the direction of the force applied?
• What distance is the boulder raised off the
  ground?

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Example 3
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Example 3
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Example 3
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Example 3
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Example 4

• Using a pulley, you lift a heavy box. The box
  has a weight of 65N. If you pull the rope a
  distance of 1m and the box moves up 0.5 m, what
  was the input force?

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Example 4
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Example 4
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Example 4
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Example 4
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Simple Machines Review

• Simple machines are helpful because they can
  increase the force you apply.
• Can the force of your hand break the metal top
  off of a metal can?a can opener can.
• Can the force of your arms cut a large branch in
  two? A hedge clipper can.

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Simple Machines Review

• Simple machines DO NOT CREATE ENERGY.
• Simple machines multiply force at the expense of
  distance.
• Work input must always equal work output.
• Energy cannot be created by a simple machine.

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Mechanical Advantage

• tells us by how much a simple machine multiplies
  the force.
• Has no units because it is a ratio
• Ideal Mechanical Advantage (IMA)
• In an ideal machine, the work out equals the
  work in.
• No energy is lost.
• IMA din/dout
• In reality, are machines actually ideal?

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Mechanical Advantage

• Actual Mechanical Advantage (AMA)
• No machine is 100 efficient
• Energy is lost to friction, wind resistance,
  heat, etc.
• AMA tells us how much our force is multiplied
  after taking energy loss into account.
• AMA Fout/Fin

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Mechanical Advantage

• When mechanical advantage is greater than 1, the
  machine increases the applied force FoutgtFin

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Example 1

• You apply 25N to a lever as you push it down a
  distance of 1.2 m. The other end of the lever is
  raised 0.6m and exerts a force of 44N on the box
  it lifts.
• What is the IMA? By how much does the lever
  increase your force if no energy is lost?
• What is AMA? By how much did this lever increase
  your force when energy is lost in the process?
• Which value is more accurate?

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Example 1 Solution

• IMA 2.0
• AMA 1.8
• AMA is more accurate

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Example 2

• A worker uses a pulley system to raise a 225N
  carton 16.5m. A force of 129N is exerted and the
  rope is pulled 33.0m.
• What is the IMA
• What is the AMA

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Example 2 Solution

• IMA 2.0
• AMA 1.7

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Efficiency

• Because energy is lost.
• Force output lower than predicted.
• Work output is lower than expected
• Ideally, work output work input
• In reality Work output is less than work input.

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Efficiency

• Efficiency is a measure of how much of the energy
  put into the system goes to do useful work.
• Efficiency (Wo/Wi) x 100
• If you put 4000J of energy into your car but only
  3000J goes toward making the car move forward,
  what is the cars efficiency?