Download Work and Power

Chapter 14
Work, Power, and
Simple Machines
Work
• Force acting through a
distance
• Must be movement
• Work = force x distance
Joule
Newton meters
Work
• If the direction of the
movement is Not the
same as the force… NO
work is done!
applied force
Motion 
Motion 
Applied force 
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
•Involves
time
Power
• How fast is work done?
• Power = Work / time
Watts Joules
seconds
• 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.
OR
 You 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 Distance
Power = Work  time
Complete the
Math Practice
on page 415
Horse- • equal to 750 watts
power
• 1 strong horse can move
a 750 N object 1 meter
in 1 second
• 1 hp = small electric
motor
• family car = 100 hp
• 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
Work
Input
• makes work easier
 increase force
 increase distance
 change the direction
• Work applied to the
machine by you
Work
•
Work
done
by
the
machine
Output


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 Force
Input Force

http://www.youtube.com/watch?v=lo_BxRD
WyRE
Ideal Mechanical Advantage
 The
mechanical advantage in the
absence of friction.
 Ideal
Mechanical Advantage =
Input Distance
Output Distance

http://www.youtube.com/watch?v=E59b5D
SJRvo
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 seesaw 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
• Eff. = Work output x 100%
Work input
Ex. Gas mileage = Miles driven
Gallons of gas
Complete the Math
Practice on Page 426.
14:4Simple
Machines
 Does
 Six
work with one movement
Types:
√ Lever
√ Inclined Plane
√ Screw
√ Wheel & Axle
√ Wedge
√ Pulley
Lever
http://www.neok12.com/video/SimpleMachines/zX7d4d664c41666974425163.htm
• bar that is free to pivot
around a fixed point called a
fulcrum
________.
•Classified in 3 categories
fulcrum is
1st class: The _______
effort
located between the ______
resistance
and the _________.
Output
Force
Input
Force
Fulcrum
Ex. Seesaw, crowbar
2nd class: The ________
resistance is
fulcrum
located between the ______
effort
and the _______.
Input
Force
Output Force
Fulcrum
 Ex. Wheelbarrow, hole punch
effort
3rd class: The ________
is
fulcrum
located between the ______
resistance
and the __________.
fulcrum
Input
Force
 Ex. Baseball bat, rake
Output
Force
Wheel and Axle
Different sized wheels
•_______
rotating together.
• Ex: door knob, tires,
can opener
Inclined Plane
http://www.neok12.com/Simple-Machines.htm
• Sloping surfa
••ce
Ex: ramp, slide
•IMA = length/height
4
4
Wedge
 An
inclined plane that moves
 Ex.
Axe, sledgehammer
Screw
http://www.neok12.com/video/SimpleMachines/zX4b56517b586556415a5a45.htm
 An
inclined plane
wrapped around a
cylinder
 Ex.
lids
Light bulb, bolts,
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.
PULLEYS
http://www.neok12.com/video/SimpleMachines/zX5c757c52524a4e59434f02.htm
Cylinder with a rope,
•_______
chain, or cable.
•Three different types
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/vid
eo/SimpleMachines/zX7a7d457d065b
790405707f.htm
Compound Machines
 Combination
of two or
more simple machines
that operate together.
 Ex. Car, watch,
washing machine