W O R K

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W O R KS I M P L EM A C H I N E S
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• The right tool for the right job.

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W O R K
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• Work is defined as a force applied over a
  distance.
• W F d
• Work in Joules (Nm) Force in Newtons (N)
  distance in meters (m)
• NOTE If the object does not move in the
  direction of the force, NO WORK IS ACCOMPLISHED.

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How much work is accomplished by moving a 600N
crate 7 m?

1. 85.7 J
2. 0.012 J
3. 4200 J
4. 593 J
5. 607 J
6. 657979.9 J

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How much work is accomplished by a 4500N
piledriver falling 25 m?

1. 180 J
2. 112500 J
3. 0.005 J
4. 4475 J
5. 4525 J
6. 3.2 x 1014 J

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How far do you have to push a 300 N crate
toaccomplish 6000 J of work?

1. 1800000 m
2. 0.05 m
3. 20 m
4. 5700 m
5. 6300 m

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Which of these unit combinations represents one
Joule of work?

1. kg?m
2. kg?m/s2
3. N?m/s2
4. kg?m2
5. N?m
6. kg 2 ?m/s2

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How much work is accomplished by an 80kg person
walking 10 m upstairs?

1. 800 J
2. 8 J
3. 0.125 J
4. 7840 J
5. 70 J
6. 90 J

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M A C H I N E S

• Machines are devices that help us accomplish
  work. They can do this by
• Redirecting a force
• Multiplying a force
• Both redirecting multiplying a force

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W O R K on M A C H I N E S

• The force you put into a machine is the Input or
  Effort Force (Fe or Fi).
• The distance the machine moves because of the
  Effort Force is the Effort Distance (de).
• The Effort Force multiplied by the Effort
  Distance gives you the Work Input (WIN) for the
  machine.
• Fe ? de WIN

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W O R K on M A C H I N E S

• The force the machine applies to another object
  is the Output or Resistance Force (Fr or Fo).
• The distance the machine moves the other object
  because of the Resistance Force is the Resistance
  Distance (dr).
• The Resistance Force multiplied by the Resistance
  Distance gives you the Work Output (WOUT) for the
  machine.
• Fr ? dr WOUT

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T R A D E O F F

• In normal operations,
• the person using the machine moves the machine
  with little force (Fe) through a large distance
  (de).
• The machine moves an object with a large force
  (Fr) over a small distance (dr).
• In essence, you are moving the machine an extra
  distance so the machine will apply extra force.

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Which force do you supply to a machine?

1. Effort Force
2. Effort Distance
3. Input Force
4. Resistance Force
5. Resistance Distance
6. Output Force

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How far does the machine move another object?

1. Effort Force
2. Effort Distance
3. Input Force
4. Resistance Force
5. Resistance Distance
6. Output Force

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Which components comprise the Work Output?

1. Effort Force
2. Effort Distance
3. Resistance Force
4. Resistance Distance

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Which of these do you increase on a machine?

1. Effort Force
2. Effort Distance
3. Resistance Force
4. Resistance Distance

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Which of these does the machine increase?

1. Effort Force
2. Effort Distance
3. Resistance Force
4. Resistance Distance

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Mechanical Advantage

• Mechanical Advantage describes the number of
  times a machine multiplies the force you apply to
  it.

MA Fo/ Fi
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What is the mechanical advantage of a machine
that applies 35 N for the 25 N of force put into
it?

1. 875
2. 0.7
3. 1.4
4. -10
5. 10

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What is the MA of a machine that applies 100 N
for the 15 N of force put into it?

1. 0.15
2. 6.7
3. 1500
4. -85
5. 85

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What is the Force Output of a machine with a MA
of 12 when you put 9 N of force into it?

1. 21 N
2. -3 N
3. 1.3 N
4. 0.75 N
5. 108 N

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Simple Machines

• A Simple Machine accomplishes the work in one
  motion.
• A Compound Machine is made up of two or more
  simple machines. Most machines are compound
  machines.

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The Lever

• A Lever is comprised of a bar that moves around a
  fixed point. The fixed point, or pivot point, is
  called the fulcrum.
• The distance from where the effort force is
  applied to the fulcrum is the Effort Arm of the
  lever.
• The distance from the fulcrum to where the
  resistance force is applied is the Resistance Arm.

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MALEVER

• The MA of a lever is calculated as
• MALever Effort Arm Resistance
  Arm
• (both in units of length, so there are no MA
  units)
• The longer the effort arm, the more the MA

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1st Class Lever

• See-Saw (Teeter-Totter)
• Prying up a lid by pushing down on a bar
• Pairs Scissors, Pliers, Hedgeclippers

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2nd Class Lever

• Door
• Wheelbarrow
• Pairs Shears, Nutcracker

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3rd Class Lever

• WARNING MA lt 1
• Increases distance, not force
• Anything you swing
• Bat, sword, stick, golf club
• Brooms, rakes, mops

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What is the MA of a lever with an Effort Arm of 6
m and a Resistance Arm of .3 m?

1. 2
2. .2
3. 1.8
4. 0.05
5. 20
6. 200

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Which type of lever does not increase the force
output of the machine?

1. 1st class
2. 2nd class
3. 3rd class
4. 4th class

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If a lever has a MA of 9, and a force of 6 N is
applied, how much force will the lever apply?

1. 0.67 N
2. 1.5 N
3. 54 N

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Wheel-and-Axle

• A simple machine made of two circles of different
  diameters that rotate together.
• The outer circle (wheel) is turned with less
  force over a larger distance so that the inner
  circle (axle) turns with more force over a
  shorter distance.

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MAWheel-and-Axle

• MA rWheel
• rAxle
• Explains how to steer larger vehicles with less
  force
• Ex. Steering wheels, door knobs, faucet handles

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What is the MA of a Wheel with a 50 cm radius
connected to an Axle with a 2.5 cm radius?

1. 125
2. 20
3. 0.05

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Pulley

• The Pulley is a simple machine comprised of a
  wheel with a rope or chain running around it.
• The MA of a pulley system is equal to the number
  of supporting ropes.

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2 Types of Pulleys

• There are two kinds of pulleys, fixed and
  moveable.
• Fixed pulleys do not move, and only redirect
  force.
• Moveable pulleys are attached to the object being
  moved and multiply force.

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The Block-and-Tackle

• A Block and Tackle system is a multiple-pulley
  system where large amounts of distance are
  converted into force.

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What is the MA of this pulley system?

1. 1
2. 2
3. 3
4. 4
5. 5
6. 6
7. 7
8. 8
9. 9
10. 10

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What is the Force Output of this pulley system?

1. 10 N
2. 100 N
3. 50 N
4. 500 N
5. 5000N

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Inclined Plane

• The Inclined Plane is a sloping surface used to
  lift objects.
• It is easier to apply a small force over the
  slope of the ramp than to lift the object
  straight up the height of the ramp.

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What is the MA of a ramp that is 12 m long but
only 4 m tall?

1. 48
2. 0.33
3. 3
4. 8

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The Wedge

• The Wedge is comprised of a moving inclined plane
  or two or more inclined planes put back-to-back.

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The Screw

• A Screw is an inclined plane wrapped around a
  cylinder.
• MA is increased by increasing the pitch (slope)
  of the threads or the number of threads per unit
  length.

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More on the screw

• A screw works when a material is pushed up the
  inclined plane formed by the threads
• As more material is in contact with the threads,
  the overall amount of friction increases
• Screws pull objects together (apart) and can hold
  more force than a nail of equal size

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2 Types of Simple Machines?

• In essence, the pulley and the wheel-and-axle are
  types of levers
• The wedge and screw are types of inclined planes

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What is the function of an inclined plane?

1. Slide objects
2. Raise objects up
3. Transport objects over a long distance

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What is the MA of an inclined plane with a height
of 3 m and a length of 6 m?

1. 3
2. 20
3. 0.5
4. 9
5. 2

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Which type of pulley multiplies force?

1. Fixed
2. Taffy
3. Moveable
4. Shank

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What is the MA of a handle with a diameter of 9
cm if the post has a diameter of 3 cm?

1. 27
2. 12
3. 6
4. 3
5. 0.333

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Which of these is an example of a lever?

1. Inclined Plane
2. Pulley
3. Wedge
4. Screw
5. Knife edge
6. Bolt

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Which of these is an example of an inclined plane?

1. Wheel-and-Axle
2. Pulley
3. 2nd Class lever
4. Wedge
5. Bicycle

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Efficiency

• Describes how well machine converts the energy
  put into it
• Always shown as a percentage
• 100 efficient means that all of the energy put
  into the machine is applied to the object being
  worked on

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2nd Law of Thermodynamics

• States that whenever energy is converted from one
  form to another, some energy is always lost as
  heat due to friction
• ? no machine can be 100 efficient (an Ideal
  Machine)

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Efficiency Formula

• WOUTPUT Fr x dr
• WINPUT Fe x de
• If you wind up with an answer at more than 100,
  you have your fraction upside-down

X 100
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Converting percentages

• A whole number becomes a decimal out of 100
• 48 0.48 6 0.06
• A decimal becomes a whole number, adding the
  percentage sign
• 0.21 21 0.75 75

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What is the efficiency of a machine that produces
89 J of work for the 100 J of work put into it?

1. 8900 J2
2. 1.12
3. 0.89
4. 112
5. 89

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What is the efficiency of a machine that produces
6100 J of work for the 9000 J of work put into it?

1. 1.48
2. 68
3. 148
4. 0.677
5. 54900000 J2

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What is the Work Output of a 62 efficient
machine when 1000 J of work is put into it?

1. 0.62 J
2. 16.13 J
3. 620 J
4. 1612.9 J
5. 62000 J

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How much work must be put into a 21 efficient
machine to generate 34 J of useable work?

1. 7.14 J
2. 161.9 J
3. 714 J
4. 1.619 J

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P O W E R

• Power is the rate at which work is accomplished
• P W
• t

W
P
t
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Power Power Power

• Power is measured in Joules per second, called
  Watts (W)
• For the same amount of work, less time requires
  more power

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How much power applies 600 J of work in 9s?

1. 66.7 W
2. 5400 W
3. 0.015 W

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Applying 21000 W of power produces how much work
in 7 s?

1. 3000 J
2. 0.0003 J
3. 147000 J