chapter 14 work, power, and simple machines. work force acting through a distance must be movement...
TRANSCRIPT
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Chapter 14
Work, Power, and Simple Machines
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Work • Force acting through a distance
• Must be movement
• Work = force x distance
Newton
metersJoule
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• If the direction of the movement is Not the same as the force… NO work is done!
Motion
applied force
Motion Applied force
Work
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Is Work Done?
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SI unit of Work
Joule = Newton x meter
(J) = N x m
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A weight lifter lifts a 1600 newton barbell over his
head. The barbell is lifted to a height of 2.0 meters.
Calculate the work done.
Work = Force x Distance
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A student rows a boat across a still pond with a force of 72 newtons. The student travels a distance of 13 meters Calculate the
work done.
Work = Force x Distance
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Power •Involves time• How fast is work done?• Power = Work / time
Joules seconds
Watts
• Large amounts of power are measured in kilowatts
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Doing work faster requires more power.
You can increase the amount of work done in a given time.
ORYou can do a given amount of work in less time.
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SI unit of Power
Watt = Joule second(W) = J/s
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A truck pulls a trailer at a constant velocity for 100 m
while exerting a force of 480 N for 1 minute (60 s). Calculate the work done
and the power.
Work = Force x DistancePower = Work time
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Complete the Math Practice on page 415
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Horse-power
• equal to 750 watts
• 1 strong horse can move a 750 N object 1 meter in 1 second
• family car = 100 hp
• 1 hp = small electric motor
• diesel train = 10,000 hp
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Energy, Work, Power, and Energy Worksheet Answers
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Part 1: Work and Power
1. Amy uses 20-N of force to push a lawn mower 10meters. How much work does she do?
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Part 1: Work and Power
2. Frank does 2400-J of work in climbing a set of stairs. If he does the work in 6 seconds, what is his power output?
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Part 1: Work and Power
3. A girl weighing 420 Newtons takes 55 seconds to climb a flight of stairs 18 meters high. What is her power output vertically?
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Part 1: Work and Power
4. How much work does an elephant do while moving a circus wagon 20 meters with a pulling force of 200-N?
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Part 1: Work and Power
5. A 40 N force is used to push a 2.00 kg cart a distance of 5 meters. What is the work done on the cart?
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Part 1: Work and Power
6. A 900-N mountain climber scales a 100 meter cliff. How much work is done by the mountain climber?
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Part 1: Work and Power
7. A small motor does applies a 200N force over 10m in 20 seconds. What is the power of the motor in watts?
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Section 14:2
WORK AND MACHINES
Yes…machines do work
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Machine • makes work easier increase force increase distance change the directionWork
Input
Work Output
• Work applied to the machine by you
• Work done by the machine
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Work Input = Input Force x Input
Distance
Work Output = Output Force x Output
Distance
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14:3 Mechanical Advantage
Number of times a machine multiplies the force applied
Ex. Cracking Pecans
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Actual Mechanical Advantage
The mechanical advantage determined by measuring the actual forces acting on a machine.
Actual Mechanical Advantage = Output ForceInput Force
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http://www.youtube.com/watch?v=lo_BxRDWyRE
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Ideal Mechanical Advantage
The mechanical advantage in the absence of friction.
Ideal Mechanical Advantage = Input DistanceOutput Distance
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http://www.youtube.com/watch?v=E59b5DSJRvo
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A woman drives her car onto wheel ramps to perform some repairs. If she drives a distance of 1.8 meters along the ramp to raise the car 0.3 meter, what is the ideal mechanical advantage (IMA) of the wheel ramps?
IMA = Input Distance Output Distance
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Complete the Math Practice on Page 425.
1. 6 2. 10 3. 2.5 m
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Part 2: Machines and Mechanical Advantage
1.
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2.
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3.
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Part 3: Torque
The drawing above represents a wrench. The left end of the wrench is attached to a bolt. Four equal forces of 100N are applied as indicated in the drawing.
A. A 100N force would cause the most torque if it was placed at which letter above? (Why)
B. What is the torque at A
C. What is the torque at C
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4. What is the boy weight in order for the see-saw to be in equilibrium?
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5. How far is the boy from the fulcrum in the see-saw in equilibrium below?
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Efficiency • How much work input is used to create work output
Ex. Gas mileage = Miles driven
Gallons of gas
• Eff. = Work output x 100%
Work input
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Complete the Math Practice on Page 426.
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14:4Simple Machines
Does work with one movement
Six Types:√ Lever √ Wheel & Axle√ Inclined Plane √ Wedge√ Screw √ Pulley
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• bar that is free to pivot around a fixed point called a ________.fulcrum
Lever
•Classified in 3 categories
http://www.neok12.com/video/Simple-Machines/zX7d4d664c41666974425163.htm
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1st class: The _______ is located between the ______ and the _________.
fulcrum effort
resistance
Output Force
Fulcrum
Ex. Seesaw, crowbar
Input Force
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2nd class: The ________ is located between the ______ and the _______.
resistancefulcrumeffort
Input Force
Output Force
Fulcrum Ex. Wheelbarrow, hole
punch
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3rd class: The ________ is located between the ______ and the __________.resistanc
e
fulcrum
effort
Input Force
Output Force
fulcrum
Ex. Baseball bat, rake
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Wheel and Axle•_______ sized wheels
rotating together.
• Ex: door knob, tires, can opener
Different
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• Sloping surfa
•ce• Ex: ramp, slide
•IMA = length/height
4 45 12
Inclined Planehttp://www.neok12.com/Simple-Machines.htm
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Wedge
An inclined plane that moves
Ex. Axe, sledgehammer
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Screw
An inclined plane wrapped around a cylinder
Ex. Light bulb, bolts, lids
http://www.neok12.com/video/Simple-Machines/zX4b56517b586556415a5a45.htm
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Let’s make our own screw Take out a sheet of
paper. Fold it at an angle. Tear along the crease. Slowly wrap it around
your pen or pencil. Turn your pen/pencil.
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•_______ with a rope, chain, or cable.
•Three different types
Cylinder
PULLEYShttp://www.neok12.com/video/Simple-Machines/zX5c757c52524a4e59434f02.htm
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Fixed Pulley•A wheel is
attached in a fixed location.
•Rotate in place.
•Ex. flagpole
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Movable Pulley
•Attached to the moving
object.
•Ex. Sails
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Pulley System
•Combines fixed and movable pulleys
•Ex. Crane
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http://www.neok12.com/video/Simple-Machines/zX7a7d457d065b790405707f.htm
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Compound MachinesCombination of two
or more simple machines that operate together.
Ex. Car, watch, washing machine