Project Project View the several objects on the View the several objects on the designated lab tables. designated lab tables. Which of these objects contain Which of these objects contain energy? What type of energy do energy? What type of energy do they contain? they contain? Which of these objects contain no Which of these objects contain no energy? energy? Based on your answers, what would Based on your answers, what would be your definition of energy? be your definition of energy?
Transcript
ProjectProject
View the several objects on the View the several objects on the designated lab tables.designated lab tables.
Which of these objects contain energy? Which of these objects contain energy? What type of energy do they contain?What type of energy do they contain?
Which of these objects contain no energy?Which of these objects contain no energy? Based on your answers, what would be Based on your answers, what would be
your definition of energy?your definition of energy?
Lesson #58Lesson #58Topic: Intro to EnergyTopic: Intro to Energy
Objectives: Objectives: (After this class I will be able to)(After this class I will be able to)
1. Describe different types of energy.1. Describe different types of energy.
3/5/07
Which of the following objects does not contain any energy?
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Rock
Apple
Rubbe
r ban
d
Bat
tery
Woo
d blo
ck
All
of thes
e th
ings
c..
0% 0% 0%0%0%0%
1.1. RockRock
2.2. AppleApple
3.3. Rubber bandRubber band
4.4. BatteryBattery
5.5. Wood blockWood block
6.6. All of these things All of these things can have energy.can have energy.
Which of the following statements is most true about energy?
0 of 20 O
nly p
artic
les
with m
...
Only
par
ticle
s th
at a
r...
Ener
gy is
som
ethin
g ..
Ener
gy ca
nnot b
e cr
e...
0% 0%0%0%
1.1. Only particles with Only particles with mass have energy.mass have energy.
2.2. Only particles that are Only particles that are moving have energy.moving have energy.
3.3. Energy is something Energy is something we are running out of.we are running out of.
4.4. Energy cannot be Energy cannot be created or destroyed.created or destroyed.
Which of the following are mostly Which of the following are mostly related to “Mechanical” Energy?related to “Mechanical” Energy?
Kin
etic
and P
oten
tial..
.
Chem
ical
and
Elect
ric..
Kin
etic
and C
hem
ical
...
Pote
ntial a
nd Ele
ctric
...
0% 0%0%0%
1.1. Kinetic and Kinetic and Potential energyPotential energy
2.2. Chemical and Chemical and Electrical energyElectrical energy
3.3. Kinetic and Kinetic and Chemical energyChemical energy
4.4. Potential and Potential and Electric energyElectric energy
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ProjectProject Split up into groups and research the Split up into groups and research the
following questions.following questions. What is energy?What is energy? How is energy used?How is energy used? Where does energy come from?Where does energy come from? List five ways we need energy to live.List five ways we need energy to live. List five different sources of energy.List five different sources of energy. Describe a transfer of energy from start to Describe a transfer of energy from start to
finish.finish.
Lesson #59Lesson #59Topic: Work and Potential EnergyTopic: Work and Potential EnergyObjectives: Objectives: (After this class I will be able to)(After this class I will be able to)
1.1. Describe Describe the relationship between the relationship between work and energy.work and energy.
2/13/07
Assignment: Ch 10 p 261 #1- 3
Warm Up: Warm Up: When / how do you do work?
Which is an example of doing work Which is an example of doing work onto a book?onto a book?
Hold
ing th
e bo
ok ab
...
Wal
king a
t con
stan
t ...
Pic
king
the
book o
ff t..
Thro
wing
the
book a
...
0% 0%0%0%
1.1. Holding the book Holding the book above your head.above your head.
2.2. Walking at constant Walking at constant speed with the book.speed with the book.
3.3. Picking the book off Picking the book off the floor and setting the floor and setting it back down.it back down.
4.4. Throwing the book Throwing the book across the room.across the room.
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Work and EnergyWork and Energy Work is done when an objects velocity or position is Work is done when an objects velocity or position is
changed.changed. A force,A force, F, F, was exerted on an object while the object was exerted on an object while the object
moved a distance, moved a distance, dd, as shown in the figure., as shown in the figure.
Work is equal to a constant force exerted on an object Work is equal to a constant force exerted on an object in the direction of motionin the direction of motion, times the object’s , times the object’s displacement.displacement.
Work and Energy Experiment Work and Energy Experiment Create a stack of books 5 books high.Create a stack of books 5 books high.
Use a force sensor to measure the force needed to lift a cart to Use a force sensor to measure the force needed to lift a cart to the top of the books. Record this force.the top of the books. Record this force.
Measure the distance the cart traveled. Record this distance.Measure the distance the cart traveled. Record this distance.
Repeat these procedures using a steep ramp to raise the cart Repeat these procedures using a steep ramp to raise the cart to the top of the books. Record the distance the cart moves to the top of the books. Record the distance the cart moves and the force required to move it.and the force required to move it.
Perform 3 more trials, each time making the ramp less and Perform 3 more trials, each time making the ramp less and less steep. Continue to record all data. less steep. Continue to record all data.
Multiply the force times the distance moved for each trial. Multiply the force times the distance moved for each trial.
Analyze your results. Can you predict how much force it would Analyze your results. Can you predict how much force it would require to raise the cart to the top of the books if the ramp was require to raise the cart to the top of the books if the ramp was 2m long? 2m long?
Work and EnergyWork and Energy Consider a force exerted on an object while the object Consider a force exerted on an object while the object
moves a certain distance. Because there is a net force, moves a certain distance. Because there is a net force, the object will be accelerated, the object will be accelerated, aa = = F/mF/m, and its velocity , and its velocity will increase. will increase.
In the equation 2In the equation 2ad = vad = vff22 − − vvii
22 , if you use Newton’s , if you use Newton’s
second law to replace second law to replace aa with with F/mF/m and multiply both and multiply both sides by sides by mm/2, you obtain:/2, you obtain:
The energy resulting from motion is called The energy resulting from motion is called kinetic kinetic energyenergy and is represented by the symbol and is represented by the symbol KEKE. .
Work and EnergyWork and Energy Substituting KE into the equation results
in W = KEf − KEi.
The right side is the difference, or change, in kinetic energy.The right side is the difference, or change, in kinetic energy.
The The work-energy theorem work-energy theorem states that when work is done on states that when work is done on an object, the result is a change in kinetic energy.an object, the result is a change in kinetic energy.
The work-energy theorem can be represented by the following The work-energy theorem can be represented by the following equation.equation.
Work is equal to the change in kinetic energy.Work is equal to the change in kinetic energy.
Using the previous equations, what Using the previous equations, what are the units of Work?are the units of Work?
N m
N m
2 N
/m K
g m
0% 0%0%0%
1.1. N mN m
2.2. N mN m22
3.3. N/mN/m
4.4. Kg mKg m
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Using the previous equations what Using the previous equations what are the units of kinetic energy?are the units of kinetic energy?
N m
2/s2
Kg m
2/s2
Kg m
/s2
N m
2/s
The
sam
e as
the
units...
0% 0% 0%0%0%
1.1. N mN m22/s/s22
2.2. Kg mKg m22/s/s22
3.3. Kg m/sKg m/s22
4.4. N mN m22/s/s
5.5. The same as the The same as the units for work.units for work.
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Work and EnergyWork and Energy We call the abnormally large unit of energy a We call the abnormally large unit of energy a JouleJoule
1J = 1 N m = 1kg m1J = 1 N m = 1kg m22/s/s22
Lifting a 1N apple 2 meters above the ground requires 2 Joules of Lifting a 1N apple 2 meters above the ground requires 2 Joules of work / energy.work / energy.
Through the process of doing work, energy can move between the Through the process of doing work, energy can move between the external world and the system.external world and the system.
The direction of energy transfer can go both ways. If the external The direction of energy transfer can go both ways. If the external world does work on a system, then world does work on a system, then WW is positive and the energy of the is positive and the energy of the system increases. system increases.
If, however, a system does work on the external world, then If, however, a system does work on the external world, then W W is is negative and the energy of the system decreases. negative and the energy of the system decreases.
Two identical cannons each fire the Two identical cannons each fire the same cannon ball. Which cannon same cannon ball. Which cannon
will fire farther?will fire farther?
0 of 20 The
longer
bar
rel c
...
The
shorte
r bar
rel c
...
Sam
e di
stan
ce
I hav
e no id
ea
0% 0%0%0%
1.1. The longer barrel The longer barrel cannoncannon
2.2. The shorter barrel The shorter barrel cannoncannon
3.3. Same distanceSame distance
4.4. I have no ideaI have no idea
Work Examples: Work Examples:
Each cannon ball exerts the same amount Each cannon ball exerts the same amount of force, however the longer barrel will exert of force, however the longer barrel will exert that force for a longer distance.that force for a longer distance.
The longer barrel cannon does more work The longer barrel cannon does more work onto the cannon ball. onto the cannon ball.
This results in a greater change in kinetic This results in a greater change in kinetic energy of the cannon ball.energy of the cannon ball.
Greater kinetic energy is equivalent to Greater kinetic energy is equivalent to greater velocity.greater velocity.
Calculating WorkCalculating Work Work can be done by each force acting on Work can be done by each force acting on
an object.an object. The total work done onto an object is the The total work done onto an object is the
sum of all the work done by each sum of all the work done by each individual force acting on the object.individual force acting on the object.
You can also find the total work done by You can also find the total work done by finding the net force acting on an object finding the net force acting on an object and multiplying it by the object’s and multiplying it by the object’s displacement.displacement.
Work Examples Work Examples Example #1: A student lifts a 1kg book 1m off of Example #1: A student lifts a 1kg book 1m off of
the floor at constant speed.the floor at constant speed. What is the total work done onto the book?What is the total work done onto the book?
What is the work done onto the book by the What is the work done onto the book by the student?student?
What is the work done onto the book by gravity?What is the work done onto the book by gravity?
Work Examples Work Examples Example #2: The student then begins walking 30m Example #2: The student then begins walking 30m
down the hall to his next class. His steady walking down the hall to his next class. His steady walking speed through the hall is 2m/s.speed through the hall is 2m/s.
What is the work done onto the book by the student What is the work done onto the book by the student when he begins to walk?when he begins to walk?
What is the work done onto the book by the student What is the work done onto the book by the student when he slows down to a stop?when he slows down to a stop?
What is the total work done onto the book from being at What is the total work done onto the book from being at rest in the first class to being at rest in the second rest in the first class to being at rest in the second class?class?
Work Examples Work Examples Example #3: The student then sets his book Example #3: The student then sets his book
down onto the floor next to his desk in the down onto the floor next to his desk in the second class. He lowers the1kg book 1m at second class. He lowers the1kg book 1m at constant speed.constant speed.
What is the total work done onto the book?What is the total work done onto the book?
What is the work done onto the book by the What is the work done onto the book by the student?student?
What is the work done onto the book by gravity?What is the work done onto the book by gravity?
Calculating work Calculating work
Calculating Work Calculating Work Other agents exert forces on the pushed car as well.Other agents exert forces on the pushed car as well. Earth’s gravity acts downward, the ground exerts a Earth’s gravity acts downward, the ground exerts a
normal force upward, and friction exerts a horizontal normal force upward, and friction exerts a horizontal force opposite the direction of motion. force opposite the direction of motion.
The upward and downward forces are perpendicular to the direction of motion and do no work. For these forces, θ = 90°, which makes cos θ = 0, and thus, W = 0.
Calculating Work Calculating Work The work done by friction acts in the direction The work done by friction acts in the direction
opposite that of motion—at an angle of 180°. opposite that of motion—at an angle of 180°. Because cos 180° = −1, the work done by Because cos 180° = −1, the work done by friction is negative. friction is negative.
Negative work done by a force exerted by Negative work done by a force exerted by something in the external world reduces the something in the external world reduces the kinetic energy of the system.kinetic energy of the system.
Positive work done Positive work done by a force increases by a force increases the kinetic energy.the kinetic energy.
A 105-g hockey puck is sliding across the ice. A player exerts a constant 4.50-N force over a distance of 0.150 m. How much work does the player do on the puck? What is
the change in the puck’s energy?
6.7
5J
0.6
75J
15.
75J
0.0
157J
0% 0%0%0%
1.1. 6.75J6.75J
2.2. 0.675J0.675J
3.3. 15.75J15.75J
4.4. 0.0157J0.0157J
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If you ride a bicycle on a 100-m long road If you ride a bicycle on a 100-m long road inclined at 25inclined at 25°°, applying a constant force of , applying a constant force of
40 N, find the work done by you.40 N, find the work done by you.
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0% 0%0%0%
A.A. (40 N) (100 m)(40 N) (100 m)
B.B. (40 N) (100 m) sin 25(40 N) (100 m) sin 25°°
C.C. (40 N) (100 m) cos 25(40 N) (100 m) cos 25°°
D.D. (40 N) (100 m) tan 25(40 N) (100 m) tan 25°°
A 4-N soccer ball sits motionless on a field. A player’s foot A 4-N soccer ball sits motionless on a field. A player’s foot exerts a force of 5 N on the ball for a distance of 0.1 m, and exerts a force of 5 N on the ball for a distance of 0.1 m, and the ball rolls a distance of 10 m. How much kinetic energy the ball rolls a distance of 10 m. How much kinetic energy
does the ball gain from the player?does the ball gain from the player?
0.5
J 0
.9 J
9 J
.05
J
0% 0%0%0%
A.A. 0.5 J0.5 J
B.B. 0.9 J0.9 J
C.C. 9 J9 J
D.D. .05 J.05 J
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The diagram shows a box being pulled by a rope The diagram shows a box being pulled by a rope with a force of 200.0 N along a horizontal surface. with a force of 200.0 N along a horizontal surface. The angle the rope makes with the horizontal is The angle the rope makes with the horizontal is 45°. Calculate the work done on the box to pull it a 45°. Calculate the work done on the box to pull it a distance of 5.0 m.distance of 5.0 m.
0
0
20
52.
5J
250
J 5
25J
707
J
0% 0%0%0%
1.1. 52.5J52.5J
2.2. 250J250J
3.3. 525J525J
4.4. 707J707J
Bonus Activity DescriptionBonus Activity Description You will receive 1 bonus point per M&M You will receive 1 bonus point per M&M
consumed and burned off (10 M&M limit). consumed and burned off (10 M&M limit). Example: You choose to eat 4 M&M’s and you Example: You choose to eat 4 M&M’s and you
answer all questions accurately and burn off all answer all questions accurately and burn off all 4 M&M’s by the end of the period, you will 4 M&M’s by the end of the period, you will receive 4 bonus points.receive 4 bonus points.
However, you must burn off all consumed However, you must burn off all consumed energy by the end of the period. Failing to do energy by the end of the period. Failing to do so will result in so will result in zerozero bonus points. bonus points.
Example: Eating 4 M&M’s and only burning off Example: Eating 4 M&M’s and only burning off 3 of them by the end of the period. 3 of them by the end of the period.
Bonus ActivityBonus Activity
We eat food everyday to gain We eat food everyday to gain potential potential energyenergy..
We then use this energy on doing We then use this energy on doing workwork.. Today you will see how much work you Today you will see how much work you
have to do to use all of the potential have to do to use all of the potential energy of the food you eat. energy of the food you eat.
On a separate sheet of paper, answer the On a separate sheet of paper, answer the following questions.following questions.
Bonus ActivityBonus Activity
1.1. How many M&M’s would you like to eat?How many M&M’s would you like to eat?2.2. There are 210 food Calories in ¼ cup of There are 210 food Calories in ¼ cup of
M&M’s. If there are 48 M&M’s in ¼ cup, M&M’s. If there are 48 M&M’s in ¼ cup, How many food calories are in 1 M&M?How many food calories are in 1 M&M?
3.3. If there are 1000 heat calories in 1 food If there are 1000 heat calories in 1 food calorie, how many heat calories are in 1 calorie, how many heat calories are in 1 M&M?M&M?
4.4. If there is 4.185 Joules of energy in 1 If there is 4.185 Joules of energy in 1 heat calorie, how many Joules of energy heat calorie, how many Joules of energy are in 1 M&M?are in 1 M&M?
Bonus ActivityBonus Activity
5.5. How many Joules of potential energy did How many Joules of potential energy did you just consume?you just consume?
6.6. What is your mass in kilograms? (divide What is your mass in kilograms? (divide your weight in pounds by 2.2)your weight in pounds by 2.2)
7.7. How much work is done by lifting your How much work is done by lifting your weightweight 0.45 meters? (the height of your 0.45 meters? (the height of your chair)chair)
8.8. How many times do you have to step up How many times do you have to step up onto your chair to burn off the M&M’s?onto your chair to burn off the M&M’s?(Divide the answer to #5 by the answer (Divide the answer to #5 by the answer to #7)to #7)
ProjectProject Explain the transfer of energy of a block Explain the transfer of energy of a block
falling to the floor.falling to the floor. What is doing work when the block is What is doing work when the block is
falling?falling? What is doing work when the block hits the What is doing work when the block hits the
ground?ground? How does the kinetic energy of the block How does the kinetic energy of the block
change from beginning to end?change from beginning to end?
Lesson #60Lesson #60Topic: Gravitational PETopic: Gravitational PE
Objectives: Objectives: (After this class I will be able to)(After this class I will be able to)
Warm Up: #1 What is the equation for the amount of work a force does on an object? #2 What is the equation for the total work done onto an object? #3 If an object starts from rest and finishes at rest, what is the total work done onto the object?#4 What is the total work done on an object moving at constant speed?
What is the equation for the amount of work a force does on an object?
W=F
d
W=
0.5m
v2
0% 0%0%0%
1.1. W=FdW=Fd
2.2. W=FdcosW=Fdcosθθ
3.3. W=W=ΔΔKEKE
4.4. W= 0.5mvW= 0.5mv22
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What is the equation for the total What is the equation for the total work done onto an object?work done onto an object?
W=F
d
W=0
.5m
v2
0% 0%0%0%
1.1. W=FdW=Fd
2.2. W=FdcosW=Fdcosθθ
3.3. W=W=ΔΔKEKE
4.4. W=0.5mvW=0.5mv22
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If an object starts at rest and If an object starts at rest and finishes at rest, what is the total finishes at rest, what is the total
work done onto the object?work done onto the object?
Dep
ends
on the
dist
...
Dep
ends
on the
forc
e...
Both
of t
hese
0 J
of w
ork
0% 0%0%0%
1.1. Depends on the Depends on the distance moveddistance moved
2.2. Depends on the Depends on the force acting on itforce acting on it
3.3. Both of theseBoth of these
4.4. 0 J of work0 J of work
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If an object is moving at constant If an object is moving at constant speed, what is the total work done speed, what is the total work done
onto the object?onto the object?
Dep
ends
on the
dist
...
Dep
ends
on the
forc
e...
Both
of t
hese
0 J
of w
ork
0% 0%0%0%
1.1. Depends on the Depends on the distance moveddistance moved
2.2. Depends on the Depends on the force acting on itforce acting on it
3.3. Both of theseBoth of these
4.4. 0 J of work0 J of work
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Potential EnergyPotential Energy An object that has the ability to do something An object that has the ability to do something
has potential energy.has potential energy. A block at rest on a 1m high desk has the A block at rest on a 1m high desk has the
potential to fall due to the force of gravity.potential to fall due to the force of gravity. If the block has a mass of 1kg, gravity could If the block has a mass of 1kg, gravity could
“potentially” do ______ J of work onto the block.“potentially” do ______ J of work onto the block. This is how much This is how much Gravitational potential Gravitational potential
energyenergy the block has while at rest on top of the the block has while at rest on top of the desk.desk.
A common shortcut to find the gravitational PE A common shortcut to find the gravitational PE of an object is PEof an object is PEgg=mgh. =mgh.
Where h is the objects height above the ground. Where h is the objects height above the ground.
What is the gravitational potential What is the gravitational potential energy of a 20kg boulder sitting on energy of a 20kg boulder sitting on
a 50m high cliff?a 50m high cliff?
0% 0%0%0%
1.1. 200N200N
2.2. 1,000J1,000J
3.3. 10,000J10,000J
4.4. 0 J0 J
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A 1000kg car is at the top of an 30A 1000kg car is at the top of an 30°° incline that is 40m long. What is the incline that is 40m long. What is the car’s gravitational potential energy? car’s gravitational potential energy?
0% 0%0%0%
1.1. 20,000J20,000J
2.2. 40,000J40,000J
3.3. 200,000J200,000J
4.4. 400,000J400,000J
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ProjectProject
With your partner, create a list of simple or With your partner, create a list of simple or complex machines you use daily. complex machines you use daily.
Do you think these machines are efficient Do you think these machines are efficient or inefficient? (in terms of energy put in or inefficient? (in terms of energy put in and work that gets done.)and work that gets done.)
Lesson #61Lesson #61Topic: Machines, Power, and EfficiencyTopic: Machines, Power, and Efficiency
Objectives: Objectives: (After this class I will be able to)(After this class I will be able to)
1.1. Explain what makes a machine efficient and Explain what makes a machine efficient and powerful. powerful.
3/20/07
Assignment: “Machines and Power” due Thursday
Warm Up: #1 How does a ramp make it easier to lift an object? What other simple machines could be used to lift a heavy object?
Simple MachinesSimple Machines You wish to lift a 100kg crate into the bed You wish to lift a 100kg crate into the bed
of a pickup that is 1.5m above the of a pickup that is 1.5m above the ground. Explain how the following ground. Explain how the following machines makes this task easier.machines makes this task easier.
1.1. Push the crate up a ramp. Push the crate up a ramp.
2.2. Use a fulcrum and lever.Use a fulcrum and lever.
3.3. Use a pulley system. Use a pulley system.
Simple MachinesSimple Machines
Example #1Example #1
1.1. Push the crate up a ramp. Push the crate up a ramp.
The crate is 100kg, the height of the truck isThe crate is 100kg, the height of the truck is
1.5m, the length of the ramp is 10m. How 1.5m, the length of the ramp is 10m. How
much force do you have to exert to push the much force do you have to exert to push the
crate up the ramp? crate up the ramp?
Simple MachinesSimple Machines
Example #2Example #2
2.2. Use a lever and fulcrum. Use a lever and fulcrum.
The crate is 100kg, the height of the truck isThe crate is 100kg, the height of the truck is
1.5m, you push the opposite end of a lever 1.5m, you push the opposite end of a lever
down 10m. With how much force do you down 10m. With how much force do you
have to push down on the opposite end of have to push down on the opposite end of
the lever?the lever?
You use a pulley system such that you pull You use a pulley system such that you pull 10m of rope out of the pulley system to lift 10m of rope out of the pulley system to lift the crate. How much force do you have to the crate. How much force do you have to
exert onto the rope? (Example #3)exert onto the rope? (Example #3)
0% 0%0%0%
1.1. 1500N1500N
2.2. 1500J1500J
3.3. 150J150J
4.4. 150N150N
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EfficiencyEfficiency This example is true for ideal situations, This example is true for ideal situations,
however no machine is 100% efficient. however no machine is 100% efficient. In all of the previous examples, we would In all of the previous examples, we would
have to exert more than 150N because the have to exert more than 150N because the efficiency of the machines would be less efficiency of the machines would be less than 100%than 100%
The amount of ideal work done compared The amount of ideal work done compared to the amount of actual work done is the to the amount of actual work done is the machines efficiency.machines efficiency.
% efficiency = ideal / actual * 100% efficiency = ideal / actual * 100
EfficiencyEfficiency When using the ramp, the actual force When using the ramp, the actual force
exerted pushing the crate was 200N. What exerted pushing the crate was 200N. What is the % efficiency of the ramp?is the % efficiency of the ramp?
The efficiency of the pulley system used to The efficiency of the pulley system used to lift the crate is 50%. What was the actual lift the crate is 50%. What was the actual
force exerted onto the rope?force exerted onto the rope?
150
N 7
5N 2
00N
300
N
0% 0%0%0%
1.1. 150N150N
2.2. 75N75N
3.3. 200N200N
4.4. 300N300N
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ProjectProject
Vote on the most powerful person in the Vote on the most powerful person in the class.class.
The top 5 will compete in several different The top 5 will compete in several different competitions. competitions.
Based on the competitions, who do you Based on the competitions, who do you think was most powerful?think was most powerful?
Why?Why?
PowerPower PowerPower is the rate in which work is done onto an is the rate in which work is done onto an
object. object. A powerful machine is one that can do a large A powerful machine is one that can do a large
quantity of work onto an object in a short amount quantity of work onto an object in a short amount of time.of time.
Fvt
Fd
t
WP
time
WorkPower
Ron and Stan are both 2m tall. Ron can lift Ron and Stan are both 2m tall. Ron can lift 40kg over his head in 2 seconds. Stan can 40kg over his head in 2 seconds. Stan can lift 30kg over his head in 1 second. Who is lift 30kg over his head in 1 second. Who is
more powerful?more powerful?
0% 0%0%0%
1.1. RonRon
2.2. StanStan
3.3. They’re the sameThey’re the same
4.4. Not enough info.Not enough info.
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Work ReviewWork Review Tommy lifts up a 10kg crate with constant Tommy lifts up a 10kg crate with constant
speed 2 m from the floor. He then holds speed 2 m from the floor. He then holds the crate at that height as he walks 20 m the crate at that height as he walks 20 m down the hall. He then sets the crate down down the hall. He then sets the crate down with a constant speed onto a 1m tall table.with a constant speed onto a 1m tall table.
What is the total work done onto What is the total work done onto the crate by Tommy?the crate by Tommy?
0J
100
J 2
00J
230
0J
57%
0%
29%
14%
1.1. 0J0J
2.2. 100J100J
3.3. 200J200J
4.4. 2300J2300J
What is the total work done onto What is the total work done onto the crate by gravity?the crate by gravity?
0J
100
J
-100
J
-200
J
0% 0%
86%
14%
1.1. 0J0J
2.2. 100J100J
3.3. -100J-100J
4.4. -200J-200J
What is the total work done onto What is the total work done onto the crate?the crate?
0J
100
J
-100
J 2
00J
100%
0%0%0%
1.1. 0J0J
2.2. 100J100J
3.3. -100J-100J
4.4. 200J200J
Work ReviewWork Review
Joey pulls a 15 kg sled across a snowy Joey pulls a 15 kg sled across a snowy field with a rope. The force of friction field with a rope. The force of friction acting on the sled is 10 N. The sled acting on the sled is 10 N. The sled accelerates across the field at a rate of 2 accelerates across the field at a rate of 2 m/sm/s22. If the sled is pulled a distance of . If the sled is pulled a distance of 30m…(hint, find the applied force by 30m…(hint, find the applied force by Joey before going on)Joey before going on)
How much work is done on the sled How much work is done on the sled by Joey?by Joey?
300
J 9
00J
120
0J
450
0J
0%
14%
86%
0%
1.1. 300J300J
2.2. 900J900J
3.3. 1200J1200J
4.4. 4500J4500J
How much work is done on the sled How much work is done on the sled by friction?by friction?
-300
J 3
00J
120
0J
-120
0J
100%
0%0%0%
1.1. -300J-300J
2.2. 300J300J
3.3. 1200J1200J
4.4. -1200J-1200J
What is the total work done onto What is the total work done onto the sled ?the sled ?
-300
J 0J
900
J
120
0J
0% 0%
100%
0%
1.1. -300J-300J
2.2. 0J0J
3.3. 900J900J
4.4. 1200J1200J
Work Review 2Work Review 2 Grimmy pushes Granny in her wheelchair Grimmy pushes Granny in her wheelchair
up a 20m long ramp that has an incline of up a 20m long ramp that has an incline of 30°. Granny has a mass of 50kg.30°. Granny has a mass of 50kg.
What is the ideal force Grimmy has to What is the ideal force Grimmy has to push?push?
If he actually has to push with a force of If he actually has to push with a force of 300, what is the efficiency of the ramp?300, what is the efficiency of the ramp?
Traffic Ticket You are driving your car uphill along a straight road.
Suddenly, you see a car run a red light and enter the intersection just ahead of you. You slam on your brakes and skid in a straight line to a stop, leaving skid marks 100 feet long. A policeman observes the whole incident and gives a ticket to the other car for running a red light. He also gives you a ticket for exceeding the speed limit of 30 mph. When you get home, you read your physics book and estimate that the coefficient of kinetic friction between your tires and the road was 0.60, and the coefficient of static friction was 0.80. You estimate that the hill made an angle of about 10owith the horizontal. You look in your owner's manual and find that your car weighs 2,050 lbs. Will you fight the traffic ticket in court?
Lesson #62Lesson #62Topic: Conservation of EnergyTopic: Conservation of EnergyObjectives: Objectives: (After this class I will be able to)(After this class I will be able to)
1.1. Describe how the total energy of a Describe how the total energy of a system is conserved.system is conserved.
3/26/07
Assignment: Concept Development 8-1 due Wednesday.
Warm Up: A 1kg stone is released from rest from the top of a 45m tall cliff. What is the total energy of the stone before it is released? 1 sec after release? 2 seconds after release? 3 seconds after release?
A 1kg stone is released from rest from the top of a 45m tall cliff. What is the total energy of the stone before it is
released?
0 of 200% 0%0%0%
1.1. 45J45J
2.2. 10N10N
3.3. 450N450N
4.4. 450J450J
After falling for 1 second, what type After falling for 1 second, what type of energy does the stone have?of energy does the stone have?
Pote
ntial
Kin
etic
Both
of t
hese
Nei
ther
of t
hese
0% 0%0%0%
1.1. PotentialPotential
2.2. KineticKinetic
3.3. Both of theseBoth of these
4.4. Neither of theseNeither of these
0 of 20
After falling for 1 second, what is the After falling for 1 second, what is the height of the stone above the bottom of height of the stone above the bottom of
the cliff?the cliff?
0 of 20
0% 0%0%0%
1.1. 5m5m
2.2. 10m10m
3.3. 35m35m
4.4. 40m40m
After falling for 1 second, what is the After falling for 1 second, what is the potential energy of the stone?potential energy of the stone?
0 of 20
45J
50J
400
J 4
50J
0% 0%0%0%
1.1. 45J45J
2.2. 50J50J
3.3. 400J400J
4.4. 450J450J
After falling for 1 second, what is the After falling for 1 second, what is the velocity of the stone?velocity of the stone?
0 of 20
5m
/s
10m
/s
28m
/s
800
m/s
0% 0%0%0%
1.1. 5m/s5m/s
2.2. 10m/s10m/s
3.3. 28m/s28m/s
4.4. 800m/s800m/s
After falling for 1 second, what is the After falling for 1 second, what is the kinetic energy of the stone?kinetic energy of the stone?
0 of 20
10J
50J
400
J 4
50J
0% 0%0%0%
1.1. 10J10J
2.2. 50J50J
3.3. 400J400J
4.4. 450J450J
Conservation of EnergyConservation of Energy The total energy of the stone at any given The total energy of the stone at any given
moment is its potential energy plus its kinetic moment is its potential energy plus its kinetic energy. energy.
Total Energy = PE + KETotal Energy = PE + KE The total energy of the stone is the same at The total energy of the stone is the same at
any time along the stone’s path as it falls.any time along the stone’s path as it falls. The energy just transfers from all potential The energy just transfers from all potential
energy (at the top) to all kinetic energy (at the energy (at the top) to all kinetic energy (at the bottom). bottom).
When the object makes contact with the When the object makes contact with the ground, the energy is transferred again into ground, the energy is transferred again into several other sources (heat, sound, bouncing). several other sources (heat, sound, bouncing).
Conservation of energy exampleConservation of energy example
Observe a pendulum and describe the Observe a pendulum and describe the conservation of energy throughout the conservation of energy throughout the motion of the pendulum bob.motion of the pendulum bob.
A
B
C
D
E
At what position(s) is the energy of At what position(s) is the energy of the pendulum only potential energy?the pendulum only potential energy?
Which path will cause the ball to go the highest on the ramp?
1 2 3 4
Ther
e is
no d
iffer
ence
20% 20% 20%20%20%1. 1
2. 2
3. 3
4. 4
5. There is no difference
0 of 20
Solving problems using the Solving problems using the conservation of energyconservation of energy
Because energy is conserved, the total Because energy is conserved, the total energy of an object at an initial position is energy of an object at an initial position is equal to the total energy at any other equal to the total energy at any other position.position.
KEKEii+PE+PEii=KE=KEff+PE+PEff
½mv½mvii22+mgh+mghii= ½mv= ½mvff
22+mgh+mghff
During a hurricane, a large tree limb, with a mass During a hurricane, a large tree limb, with a mass of 22kg and a height of 13.3m above the ground, of 22kg and a height of 13.3m above the ground,
falls on a roof that is 6m above the ground.falls on a roof that is 6m above the ground.What is the kinetic energy of the limb when it hits What is the kinetic energy of the limb when it hits
the roof?the roof?
0 of 20 2
926J
160
6J
132
0J
12.
08m
/s
0% 0%0%0%
1.1. 2926J2926J
2.2. 1606J1606J
3.3. 1320J1320J
4.4. 12.08m/s12.08m/s
During a hurricane, a large tree limb, with a mass During a hurricane, a large tree limb, with a mass of 22kg and a height of 13.3m above the ground, of 22kg and a height of 13.3m above the ground,
falls on a roof that is 6m above the ground.falls on a roof that is 6m above the ground.What is the speed of the branch when it hits the What is the speed of the branch when it hits the
roof?roof?
0 of 20 1
6m/s
160
6m/s
11m
/s
12m
/s
0% 0%0%0%
1.1. 16m/s16m/s
2.2. 1606m/s1606m/s
3.3. 11m/s11m/s
4.4. 12m/s12m/s
A bike rider approaches a hill at a speed of 8.5m/s. A bike rider approaches a hill at a speed of 8.5m/s. The combined mass of the bike and the rider is The combined mass of the bike and the rider is
85kg. The rider coasts up the hill. At what height 85kg. The rider coasts up the hill. At what height will the bike come to rest?will the bike come to rest?
0 of 20 3.6
m 5
m
722
.5m
0.8
5m
0% 0%0%0%
1.1. 3.6m3.6m
2.2. 5m5m
3.3. 722.5m722.5m
4.4. 0.85m0.85m
Suppose that the bike rider pedaled up the hill and Suppose that the bike rider pedaled up the hill and comes to a stop at the top. The height of the hill is comes to a stop at the top. The height of the hill is 6m. How much work did the rider have to do to get 6m. How much work did the rider have to do to get
to the top of the hill? to the top of the hill?
0 of 20 2
040J
307
0J
510
0J 2
.4m
0% 0%0%0%
1.1. 2040J2040J
2.2. 3070J3070J
3.3. 5100J5100J
4.4. 2.4m2.4m
A skier starts from rest at the top of a 45m high hill, A skier starts from rest at the top of a 45m high hill, skis down a 30° incline into a valley, and continues skis down a 30° incline into a valley, and continues up a 40m high hill. How fast is the skier moving at up a 40m high hill. How fast is the skier moving at
the bottom of the valley? the bottom of the valley?
0 of 20 4
50m
/s
900
m/s
30m
/s
4.5
m/s
0% 0%0%0%
1.1. 450m/s450m/s
2.2. 900m/s900m/s
3.3. 30m/s30m/s
4.4. 4.5m/s4.5m/s
A skier starts from rest at the top of a 45m high hill, A skier starts from rest at the top of a 45m high hill, skis down a 30° incline into a valley, and continues skis down a 30° incline into a valley, and continues up a 40m high hill. How fast is the skier moving at up a 40m high hill. How fast is the skier moving at
the top of the second hill? the top of the second hill?
0 of 20 1
0m/s
30m
/s
40m
/s
20m
/s
0% 0%0%0%
1.1. 10m/s10m/s
2.2. 30m/s30m/s
3.3. 40m/s40m/s
4.4. 20m/s20m/s
Advanced problemAdvanced problem In a belly flop diving contest, the winner is the In a belly flop diving contest, the winner is the
diver who makes the biggest splash. The diver who makes the biggest splash. The splash is dependent not only on style, but also splash is dependent not only on style, but also on how much kinetic energy the diver has on on how much kinetic energy the diver has on impact. Consider a contest in which each impact. Consider a contest in which each contestant jumps from a 3m high diving board. contestant jumps from a 3m high diving board. One diver has a mass of 136kg and simply One diver has a mass of 136kg and simply steps off the platform. Another diver has a steps off the platform. Another diver has a mass of 102kg and leaps upward from the mass of 102kg and leaps upward from the platform. How high would the second diver platform. How high would the second diver have to leap to make a competitive splash?have to leap to make a competitive splash?
ProjectProject
A ball is launched vertically into the air A ball is launched vertically into the air with an initial speed of _______ how high with an initial speed of _______ how high did the ball go?did the ball go?
Winter Olympics You have landed a summer job with a company that has been given
the contract to design the ski jump for the next Winter Olympics. The track is coated with snow and has an angle of 25o from the horizontal. A skier zips down the ski jump ramp so that he leaves it at high speed. The winner is the person who jumps the farthest after leaving the end of the ramp. Your task is to determine the height of the starting gate above the end of the ramp, which will determine the mechanical structure of the ski jump facility. You have been told that the typical ski-jumper pushes off from the starting gate at a speed of 2.0 m/s. For safety reasons, your design should be such that for a perfect run down the ramp, the skier's speed before leaving the end of the ramp and sailing through the air should be no more than 80 km/hr. You run some experiments on various skies used by the jumpers and determine that the coefficient of static friction between the snow and the skis is 0.10 and its coefficient of kinetic friction is 0.02. Since the ski-jumpers bend over and wear very aerodynamic suits, you decide to neglect the air resistance to make your design.
Lesson #63Lesson #63Topic: Lab: Conservation of EnergyTopic: Lab: Conservation of Energy
Objectives: Objectives: (After this class I will be able to)(After this class I will be able to)
1.1. Use the conservation of energy to calculate Use the conservation of energy to calculate the velocity of a steel ball.the velocity of a steel ball.
3/28/07
Assignment: Calculate the velocity of the ball when it leaves the desk and place the target at the appropriate spot on the floor to have the ball land on the bull’s eye.
Warm Up: A ball rolls off of a 1m tall desk with an initial horizontal velocity of 1.5m/s. How far from the desk does the ball hit the ground?
A ball rolls off of a 1m tall desk with an initial horizontal velocity of 1.5m/s. How far from
