Chapter 14 Work, Power, and Simple Machines. Work Force acting through a distance Must be movement...
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Transcript of Chapter 14 Work, Power, and Simple Machines. Work Force acting through a distance Must be movement...
Chapter 14
Work, Power, and Simple Machines
Work • Force acting through a distance
• Must be movement
• Work = force x distance
Newton
metersJoule
• If the direction of the movement is Not the same as the force… NO work is done!
Motion
applied force
Motion Applied force
Work
Is Work Done?
SI unit of Work
Joule = Newton x meter
(J) = N x m
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
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
Power •Involves time• How fast is work done?• Power = Work / time
Joules seconds
Watts
• Large amounts of power are measured in kilowatts
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.
SI unit of Power
Watt = Joule second(W) = J/s
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
Complete the Math Practice on page 415
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
Energy, Work, Power, and Energy Worksheet Answers
Part 1: Work and Power
1. Amy uses 20-N of force to push a lawn mower 10meters. How much work does she do?
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?
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?
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?
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?
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?
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?
Section 14:2
WORK AND MACHINES
Yes…machines do work
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
Work Input = Input Force x Input
Distance
Work Output = Output Force x Output
Distance
14:3 Mechanical Advantage
Number of times a machine multiplies the force applied
Ex. Cracking Pecans
Actual Mechanical Advantage
The mechanical advantage determined by measuring the actual forces acting on a machine.
Actual Mechanical Advantage = Output ForceInput Force
http://www.youtube.com/watch?v=lo_BxRDWyRE
Ideal Mechanical Advantage
The mechanical advantage in the absence of friction.
Ideal Mechanical Advantage = Input DistanceOutput Distance
http://www.youtube.com/watch?v=E59b5DSJRvo
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
Complete the Math Practice on Page 425.
1. 6 2. 10 3. 2.5 m
Part 2: Machines and Mechanical Advantage
1.
2.
3.
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
4. What is the boy weight in order for the see-saw to be in equilibrium?
5. How far is the boy from the fulcrum in the see-saw in equilibrium below?
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
Complete the Math Practice on Page 426.
14:4Simple Machines
Does work with one movement
Six Types:√ Lever √ Wheel & Axle√ Inclined Plane √ Wedge√ Screw √ Pulley
• 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
1st class: The _______ is located between the ______ and the _________.
fulcrum effort
resistance
Output Force
Fulcrum
Ex. Seesaw, crowbar
Input Force
2nd class: The ________ is located between the ______ and the _______.
resistancefulcrumeffort
Input Force
Output Force
Fulcrum Ex. Wheelbarrow, hole
punch
3rd class: The ________ is located between the ______ and the __________.resistanc
e
fulcrum
effort
Input Force
Output Force
fulcrum
Ex. Baseball bat, rake
Wheel and Axle•_______ sized wheels
rotating together.
• Ex: door knob, tires, can opener
Different
• Sloping surfa
•ce• Ex: ramp, slide
•IMA = length/height
4 45 12
Inclined Planehttp://www.neok12.com/Simple-Machines.htm
Wedge
An inclined plane that moves
Ex. Axe, sledgehammer
Screw
An inclined plane wrapped around a cylinder
Ex. Light bulb, bolts, lids
http://www.neok12.com/video/Simple-Machines/zX4b56517b586556415a5a45.htm
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.
•_______ with a rope, chain, or cable.
•Three different types
Cylinder
PULLEYShttp://www.neok12.com/video/Simple-Machines/zX5c757c52524a4e59434f02.htm
Fixed Pulley•A wheel is
attached in a fixed location.
•Rotate in place.
•Ex. flagpole
Movable Pulley
•Attached to the moving
object.
•Ex. Sails
Pulley System
•Combines fixed and movable pulleys
•Ex. Crane
http://www.neok12.com/video/Simple-Machines/zX7a7d457d065b790405707f.htm
Compound MachinesCombination of two
or more simple machines that operate together.
Ex. Car, watch, washing machine