Chapter 14 Lesson 1

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Chapter 14 Lesson 1

• Work and Power

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I. Work

• A. Books in hand Demo
• B. Def the product of force and distance
• 1. Nota job, chores, school.
• 2. Formula Work Force x Distance
• 3. Force is in Newtons
• 4. Distance is in meters
• 5. Work is in Joules

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• 6. Ex Your backpack is full and weighs 30
  Newtons. You lift it from the floor to the
  shelf, a distance of 1.5 meters. How much work
  is done on the backpack?
• W F x D
• 30 N x 1.5 m ?
• ?45 Joules

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• 7. A backpack has a weight of 35 N and a student
  who is 1.8 meters tall has it on her back. How
  much work is the student doing on the backpack?
• W F x D
• 35 N x 0 meters 0 Joules

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• 8. A carpenter lifts a 45-kg beam 1.2 meters.
  Approximately how much work is done on the beam?
  (be careful!!! Look at your units)
• Hint 1 kg 9.8 N
• 45 kg x 9.8 N/kg 441 Newtons
• 441 N x 1.2 meters
• 529.2 Joules

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II. Power

• A. Def Rate of doing work.
• 1. 2 variables
• a. Work and Time
• B. Formula
• 1. Power Work (J) / Time (s)
• a. Unit is the Watt (W)
• b. A 60-watt light bulb requires 60 J per
  second.

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• C. Ex A machine puts forth 400 J of work in
  0.25 seconds. What is the amount of power of the
  machine?
• P W / T
• P 400 J

1600 Watts
0.25 Sec
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• D. A similar machine exerts 500 J of work with
  1400 Watts of power. What is the time it takes
  this machine to do its job?
• T W / P
• T 500 J

0.36 sec
1400 Watts
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Chapter 14Lesson 2

• Work and Machines

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I. Why we use Machines

• What are Machines?
• 1. Machine a device that changes a force.
• ? makes work easier
• ? change the size of a force needed
• ? change the direction of a force

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• Advantages of a Machine
• 1. Increasing force
• ?tradeoff is you put in greater distance
• -easier
• Ex. Pg. 418 changing a tire with a jack
• 2. Increasing distance
• ?tradeoff is you put in less distance
• -harder / more difficult
• Ex. Pg. 419 rowing a boat with oars
• 3. Changing Direction
• ?movement in one direction causes movement in
  the opposite direction
• Ex. Pg. 419 rowing a boat with oars

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II. Work Input and Work Output

• Work Input to a machine
• 1. Formula Fi x Di
• a. Input Force the force you exert to the
  machine.
• -Fi
• -Ex. Pushing on a crowbar
• b. Input Distance the distance the input force
  acts through.
• -Di
• -Ex. The length of a crowbar

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• Work Output of a machine
• 1. Formula Fo x Do
• 1. Output force the force exerted by the
  machine.
• Fo
• 2. Output distance the distance the output
  force is exerted through.
• Do
• Work output is always less than work input
  Why???
• ? Friction (pg. 420 p. 1 end)

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• In-class Assignment
• Pg. 420 s 1-6
• 2. Read 14.3

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Chapter 14Lesson 3

• Mechanical Advantage and Efficiency

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• I. Mechanical Advantage
• A. Def the of times a machine multiplies
  the input force. (MA)
• B. Pg. 421 nut cracker
• C. MA of Force Output force
• Input force
• D. Ideal MA w/o friction
• E. MA of Distance
• Input Distance
• Output Distance

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• F. Ex. A carpenter uses a claw hammer to pull
  a nail from a board. The nail has a resistance
  of 2500 N. The carpenter applies an input force
  of 125 N. What is the mechanical advantage of
  the hammer?
• MA Output force
• Input force
• so 2500 N
• 125 N
• 20 MA

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• G. Ex. A worker applies an input force of 20
  N to pry open a window that has a output force of
  500 N. What is the mechanical advantage of the
  crowbar?
• 500 / 20
• 25

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• H. Find the input force needed to lift a 2000
  N rock, using a jack with a mechanical advantage
  of 10.
• Fi Fo / MA
• 2000 / 10
• 200 N

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II. Efficiency

• B. Def How much work put into the machine is
  changed to useful work put out by the machine.
• 1. Formula
• Efficiency Woutput
• Winput

X 100
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• 2. Why doesnt Wout Win?
• -friction
• -dirt
• -age
• -bad parts
• -improper use

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• 3. Ex A sofa weighing 1000 N must be placed
  in a truck bed 1.2 m off of the ground. A worker
  uses a force of 500 N to push the sofa up the
  inclined plane that has a slope of 3.5 m. What
  is the efficiency of the inclined plane?
• Fo
• Fi
• Do
• Di

1000 N
500 N
1.2 m
3.5 m
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• 1000 N x 1.2 m
• 500 N x 3.5 m
• 68.6 efficient

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• A record setting buck weighing 1205 N is pulled
  up a ramp to the back of a pick-up with a force
  of 600 N by a hunter. If the back end of the
  pick up is 1.2 meters high and the length of the
  ramp is 3.2 meters, what is the efficiency of the
  ramp?

75.3
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Chapter 14Lesson 4

• The Simple Machine

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I. Lever System

• A. Def A lever is a bar that is free to pivot
  or turn about a fixed point.
• B. Parts of a lever
• 1. Fulcrum fixed point of the lever
• 2. Effort arm part where force is applied to
  the lever.
• 3. Resistance arm part where the resistance
  is found on the lever.

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• C. Ideal Mechanical Advantage
• 1. IMA Length of effort arm
• Length of resistance arm
• or
• Le
• Lr

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• 2. Ex A worker uses an iron bar to raise a
  manhole cover weighing 65 N. The effort arm of
  the lever is 60 cm long. The resistance arm is
  10 cm long. What is the ideal mechanical
  advantage of the bar?
• Le
• Lr
• 6 (IMA)

60 cm
10 cm
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• D. Types of Levers
• 1. 1st Class
• -E F R
• -Common Ex
• teeter totter
• scissors
• pliers
• claw of hammer

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• 2. 2nd Class
• - F R E
• - Common Ex
• stapler
• bottle opener
• wheelbarrow
• nut cracker

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• 3. 3rd Class (increase speed)
• - F E R
• - Common Ex
• fishing rod
• tweezers
• mousetrap
• baseball bat
• softball bat

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II. Pulleys

• A. Def a grooved wheel with a rope or chain
  running along the groove.
• 1. similar to 1st class lever
• 2. uses rope instead of bar
• 3. has effort arm and resistance arm.

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• B. Types of Pulleys
• 1. Fixed
• -Fixed pulley does not move
• -MA 1
• 2. Movable
• -Movable pulley is movable
• -MA 2 (can vary)

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• 3. Block and Tackle
• -uses fixed and
• movable
• -Large Mechanical
• advantage
• -MA of ropes in
• the pulley system
• -MA 2

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What is the MA?
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III. Wheel and Axle

• A. Def a simple machine consisting of 2
  different sized wheels that rotate together.
• 1. Parts
• -small wheel axle
• 2. Effort force is applied to large wheel
• 3. Large wheel turns the axle
• 4. IMA rw / ra
• 5. Ex Bike, doorknobs, ice cream makers, cars

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• 6. Ex An ice cream maker has a wheel radius
  of 20cm. The axle has a radius of 15 cm. What
  is the ideal mechanical advantage of the wheel
  and axle?
• 20 / 15
• 1.3 IMA

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IV. Inclined Plane, Wedge, Screw

• A. Inclined Plane
• 1. Def a sloped surface used to raise objects
• 2. IMA length of slope / height of slope
• 3. Ex any ramp
• 4. Remember Force is smaller but distance is
  greater.

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• B. Screw
• 1. Def Inclined plane wrapped in a spiral
  cylindrical post.
• 2. Ex screws, lids, drill bits

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• C. Wedge
• 1. Def Inclined plane with 1 or 2 sloping
  sides
• 2. Used to cut or split
• 3. Ex knives, ax blades, chisels