Energy

1
Energy

• Work and Power
• Simple Machines
• Kinetic Energy
• Potential Energy

2
Equations used so far . . .
3
Work and Power
4
Work

• Occurs when a force causes something to move a
  distance
• Motion must be in the same direction as the force

5
Is this an example of work?
force
distance
yes
6
Is this work?
force
Yesif he LIFTS the barbell
distance
7
Is this work?
force
distance?
Nowhy not?
8
Is this work?
force
Nowhy not?
distance
9
Work Equation

• Work Force x Distance
• W Fd

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Units for Work

• W Fd
• Or

Nm
Joules (J)
11
Practice Problem

• John uses 45 Newtons of force to push his lazy
  dog 3.2 meters across the kitchen floor. How
  much work does John do?
• F 45 N
• d 3.2 m
• W ?

W Fd
W (45 N)(3.2 m)
W 144 J s.f. 140 J
12
Power

• The rate at which work is done
• In other wordshow fast work is done
• Power Work
• time
• P W
• t

Units
Joules second
Watts (W)
13
Practice Problem

• If John takes 5.0 seconds to push his dog, what
  is his power output?
• W 144 J
• t 5.0 s
• P ?

P W/t
P 144 J/5.0 s
P 28.8 W s.f. 29 W
14
A crane uses an average force of 5200 N to lift a
girder 25 m. How much work does the crane do?
15
An apple weighing 1 N falls a distance of 1 m.
How much work is done on the apple by the force
of gravity?
16
A bicycle's brakes apply 125 N of friction force
to the wheels as the bike moves 14.0 m. How much
work do the brakes do?
17
A mechanic uses a hydraulic lift to raise a 1200
kg car 0.50 m off the ground. How much work does
the lift do on the car?
18
While rowing across the lake during a race, John
does 3960 J of work on the oars in 60.0 s. What
is his power output in watts?
19
Anna walks up the stairs on her way to class.
She weighs 565 N, and the stairs go up 3.25 m
vertically.

• A. What is her power output if she climbs the
  stairs in 12.6 s?
• B. What is her power output if she climbs the
  stairs in 10.5 s?

20
Assignment

• Practice Problems
• p. 432 1-4
• 1. 130000 J
• 2. 1 J
• 3. 1750 J
• 4. 5900 J
• p. 434 1-2
• 1.66 W
• 2a. 146 W
• 2b. 175 W

21
Review

• What does the term work mean in your everyday
  life?
• What does the term work mean in Physical
  Science?
• Work is the ability to produce a force that
  causes movement.

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Work and Power Practice Problems Mixed Equations
(Front only)

• W 237825 J
• d 0.6 m
• F 27 N
• a) P 494 watts
• b) d 3 m
• W 300 000 J

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Mixed Practice (complete the back)
Velocity
Work
Force
Acceleration
Slope
Weight
Power
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Review

• What does the term power mean in Physical
  Science?
• Power is the rate (how fast) an individual is
  able to do work.
• What are the two main families of simple
  machines?
• 1. Lever Family
• 2. Inclined Plane Family

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Household tools Mini-Lab
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Household Tools Mini-LabPurpose To relate
household tools to the six simple machines.
Tool Type of machine(s) in this tool Is the applied force transferred to another part of the tool? Which part of the tool does the work? Is the force that the tool exerts on an object greater or lesser than the force exerted on the tool? Explain.






Simple Machines Reading Guide 13.2
27
The 6 Simple Machines
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The 6 Simple Machines

• Lever Family
• Inclined Plane Family

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The Lever Family

• Lever
• Pulley
• Wheel Axle

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1. Lever

• Lever Family

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Levers-First Class

• In a first class lever the fulcrum is in the
  middle and the resistance and effort is on either
  side
• Think of a see-saw

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Levers-Second Class

• In a second class lever the fulcrum is at the
  end, with the resistance in the middle
• Think of a wheelbarrow

33
Levers-Third Class

• In a third class lever the fulcrum is again at
  the end, but the effort is in the middle
• Think of a pair of tweezers

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What's In The Middle?

• 1st Class
• 2nd Class
• 3rd Class

• Fulcrum (F)
• Resistance (R)
• Effort (E)

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Levers

• Levers make work easier by reducing the amount of
  force necessary to move a load.
• Mechanical Advantage of a lever is equal to
  effort arm divided by the resistance arm.
• MA effort
• resistance

36
2. Pulley

• Lever Family

37
Pulleys

• The pulley distributes the force of the load
  among several ropes in the system
• Using a single pulley does not multiply the input
  force, but it does change the direction of the
  input force.
• Using several pulleys increases the distance the
  of the input force causing a larger output force.
  The mechanical advantage is equal to the number
  of ropes sharing the load.
• MA of ropes-1 or MA of pulleys
• Figure 3 pg 440

38
3. Wheel and axle

• Lever Family

39
Wheel and Axle

• A wheel and axle system makes work easier by
  increasing a small amount input force applied to
  the wheel.
• Mechanical Advantage is the wheel radius divided
  by the axle radius.
• MA radius wheel
• radius axle

40
The Inclined Plane Family

• Inclined plane
• Wedge
• Screw

41
4. Inclined Plane

• Inclined Plane Family

42
Inclined Plane

• An inclined plane makes work easier by increasing
  the distance over which force is applied. Less
  input force is required to lift a load.
• Mechanical Advantage of an inclined plane is
  equal to the distance of the sloped edge divided
  by the height.
• MA slope
• height

43
5. Wedge

• Inclined Plane Family

44
Wedge

• A wedge is two inclined planes put back to back.
• Mechanical Advantage of a wedge is the slope
  length divided by the width of the wedge.
• MA slope
• width

45
6. Screw
46
Screw

• A screw is an inclined plane wrapped around a
  cylinder.
• Mechanical Advantage of a screw is length of the
  treads divided by the diameter of the cylinder.
• MA length
• diameter

47
Mechanical Advantage load effort

• MA F out
• F in

48
Work Machines
49
How do machines make work easier?

• By changing the size or direction of the FORCE
• Machines DO NOT make work less
• Force is less, therefore distance is greater
• W F d

50
Example Lever
Less force
Greater distance
51
Example Inclined Plane
Less force
Greater distance
52
Work input (Win)

• The work that the operator/user does to the
  machine
• Input force (Fin)force exerted by the user
• Input distance (din)distance covered by the user
• Win Fin x din

53
Work output (Wout)

• The work that the machine does to another object
• Output force (Fout)force exerted by the machine
• Output distance (dout)distance covered by the
  machine
• Wout Fout x dout

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Hints for solving problems

• Input Force is always less than Output force
  
• (Fin lt Fout)
• Input distance is always greater than the output
  distance
• (din gt dout)

Remember The machine operator exerts less force
but covers more distance!
55
Mechanical Advantage (MA)

• How much a machine multiplies force or distance
• Should always be greater than 1 (or it isnt a
  very good machine!)

56
Equation

• MA Fout or MA din
  Fin dout

57
Sample Problem 1

• A bus driver applies a force of 55.0 N to the
  steering wheel, which in turn applies 132 N of
  force to the steering column. What is the
  mechanical advantage of the steering wheel?
• What simple machine is being used here?

If the bus driver turns the wheel 1.40 meters,
how much work does she do?
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G U E S S
G U E S S
G U E S S
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Sample Problem 2

• Two moving men are pushing a 225 N bookcase into
  the back of a moving truck by exerting 75.0 N of
  force. The ramp is 3.00 meters long and rises
  1.00 meters to the inside of the truck. A) How
  much work do the men do? B) How much work does
  the ramp do? C) What is the mechanical
  advantage of the ramp?

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G U E S S
G U E S S
G U E S S
61
Review

• Why do we use simple machines?
• Simple machines are used to make work easier.
• List the two equations for Mechanical Advantage
• MA F out / F in
• MA d in / d out

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Thursday, October 3, 2013

• BR When you calculate Mechanical Advantage, who
  is responsible for
• Input
• Output
• EQ A student helps his teacher by lifting a
  heavy box, carrying it across the room, and
  putting it on the lab table. Did the student do
  work? When?

• Agenda
• Work and Power Lab

63
Review

• When you calculate Mechanical Advantage, who is
  responsible for
• Input
• Output
• A student helps his teacher by lifting a heavy
  box, carrying it across the room, and putting it
  on the lab table. Did the student do work? When?
• Yes, only when lifting the box because his net
  force and the movement were in the same
  direction.

64
Review

• Work
• Power

65
Review

• 6 Simple Machines
• Mechanical Advantage

66
Review

• BR What is in the middle of each class of
  lever?
• 1st
• 2nd
• 3rd
• EQ What are the appropriate equations and units
  for work and power?
• Work F x d (Joules)
• Power Work / time (watts)

67
ENERGY

• SP3. Students will relate transformations and
  flow of energy within a system.
• a. Identify energy transformations within a
  system (exmp. Lighting of a match.)

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ENERGY

• Vocabulary
• Energy
• Law of conservation of energy

• Key Concepts
• There are many different forms of energy
• Energy can change from one form to another

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(No Transcript)
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Law of Conservation of Energy

• Energy may change from one form to another, but
  total amount of energy in a system never changes.

71
Examples of Energy Transformations

• Burning a match
• Chemical energy?
• light, heat

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• Bouncing a ball
• Potential energy ? kinetic energy, sound, and heat

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How do you get energy?
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Examples

• Photosynthesis
• Light ? chemical energy

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What energy transformations take place in the
following scenario?

• A local farmer raises cattle for beef. On Friday
  night, you go out to your favorite restaurant and
  eat a hamburger.

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Heat
Light
photosynthesis
Nuclear
Heat
Chemical
Heat
Chemical
Kinetic
Kinetic
77
Review

• What forms of energy do you encounter each day?
• What energy transformations take place regularly
  in your everyday life?

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Group Potential Energy-Calculate the
gravitational potential energy of the
followingA 1,200 kg car at the top of a hill
that is 42 m high.A 65 kg climber on top of
Mount Everest (8,800 m high).

• G U E S S

79
Group Potential Energy-Calculate the
gravitational potential energy of the
followingA 0.52 kg bird flying at an altitude
of 550 m.

• G U E S S

80
Group Kinetic Energy-Calculate the kinetic energy
in joules of a 1,500 kg car that is moving at a
speed of 15 m/s.

• G U E S S

81
Review

• Kinetic energy is displayed while an object is __
  ____.
• IN MOTION
• List the equation for calculating Kinetic Energy
  and provide the appropriate triangle.
• KE ½ mv 2

82
Review

• Potential energy is displayed due to an objects
  ____.
• POSITION
• List the equation for calculating Potential
  Energy and provide the appropriate triangle.
• PE mgh

83
Review

• Answer the following based on yesterdays lab
• When you drop a ball, where does it have the
  greatest amount of . . .
• Potential energy? 
• At the top just before it is released
• Kinetic energy? 
• At the bottom just as it hits the ground
• List the equation for calculating velocity using
  Kinetic Energy.
• . KE .
• V (1/2)m

 
84
Review

• A skydiver prepares to jump out of a plane. At
  what point will she have the greatest kinetic
  energy? potential energy?
• The greatest kinetic energy occurs at the lowest
  point-just before she reaches the ground.
• The greatest potential energy occurs just at the
  highest point-just before she begins to jump out
  of the plane
• Describe the energy transformation-Ms. Berrie
  turns her projector on and shows the movie
  Osmosis Jones to her students.
• Electrical ? light sound

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Energy Problems

• Energy Test-
• Calculating Velocity

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Additional Group Practice

• You drop a 2 kg watermelon from a 5m tall
  ladder. How fast is the melon traveling when it
  strikes the ground?
• G U E S S

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Additional Group Practice

• You drop a 0.250 kg baseball from a height of 6
  m. How fast is the ball traveling when it
  strikes the ground?
• G U E S S

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Additional Group Practice

• After 10 s of free-fall, a 70 kg skydiver has
  30.5 J of kinetic energy. How fast is he
  traveling towards earth at that instant?
• G U E S S

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Additional Group Practice

• After 120 s of free-fall, the same 70 kg skydiver
  has 220 J of kinetic energy. How fast is he
  traveling towards earth?
• G U E S S

90
Individual Practice

• How fast is a 0.35 kg ball traveling as it hits
  the ground if it is dropped a total distance of 2
  m?
• A 30 kg cannon ball is shot from a cannon and
  reaches a maximum of 410 J of kinetic energy.
  How fast is it travelling at that particular
  moment?
• A welder working on a new office building drops
  his construction hat as he reaches the top of the
  50 m building. If the mass of the hat is 1.5 kg,
  how fast is the hat travelling when it hits the
  ground?

91
Review

• BR Based on the law of conservation of energy,
  what do you know about the total potential energy
  at the top of a fall and the total kinetic energy
  at the bottom of a fall?
• The total amount of energy remains the same.
• PE top KE bottom
• EQ Describe the following energy transformation
  
• Mrs. Molyson drinks a cup of Gatorade then runs a
  5k.
• Chemical ? Kinetic

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Roller Coaster Review Part I
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Review

• Based on the law of conservation of energy, what
  do you know about the total potential energy at
  the top of a fall and the total kinetic energy at
  the bottom of a fall?
• The total amount of energy remains the same.
• PE top KE bottom
• Describe the following energy transformation
• Mrs. Molyson drinks a cup of Gatorade then runs a
  5k.
• Chemical ? Kinetic

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Study Guide Work, Power, Machines, Energy
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Equations
Kinetic Energy Potential Energy

• Work
• Power
• Mechanical Advantage

96
Review

• List the 3 requirements for work.
• Force
• Distance
• F d must be in the same direction.

97
Review

• Where would you expect the greatest KE?
  greatest PE?
• KE ___________
• PE ___________
• A measure of the amount of KE in a material is
  ____
• HEAT / TEMPERATURE