Transcript Chapter 4 Section 1 Energy

Chapter 4 Section 1
Energy
Page 99 - 105
Energy Definition
• Energy is the ability to cause change ????
• Energy is the ability to do work.
• Work is moving something against a force.
– Force and distance
• If we lift a block of metal from the floor to this
table, we have done work on the block.
– What is the force?
• If we push a box across the floor we do work.
– What is the force
Different Types of Energy
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Mechanical
Electrical
Chemical
Sound
Light
Thermal (heat)
Nuclear
Energy Conversion
• Chemical Energy to Mechanical Energy
– Burn gasoline in a car to make it go
• Chemical Energy to Electrical Energy
– A battery supplies power to a cell phone
•
•
•
•
•
Electrical Energy to Light Energy - ?
Electrical Energy to Sound Energy - ?
Electrical Energy to Mechanical Energy-?
Chemical energy to Thermal Energy
Electrical Energy to Thermal Energy
Kinetic Energy
• The energy something has as a result of its motion
• KE = ½ m v2
• m = mass
v = velocity
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•
v2= 1 m2/s2
v2= 4 m2/s2
v2= 9 m2/s2
v2= 16 m2/s2
v2= 25 m2/s2
v = 1 m/s
v = 2 m/s
v = 3 m/s
v = 4 m/s
v = 5 m/s
Energy Units
• Energy is the same as work
• KE= ½ m v2
– m in kg, v in m/s so v2 is m2/s2
– or (kg m/s2 )* m or N * m called a joule
• W=Fd
– F: Newtons Kg m/s2
– d : meters m
– W : N m called a joule
• Kg m2 / s2 called a joule J
Practice Problems – Kinetic Energy
(Page 102: 1,2,3)
• A jogger with a mass of 60.0 kg is moving at a
speed of 3.0 m/s. What is the jogger’s kinetic
energy?
• Given:
• Asked:
• Formula: KE = ½ mv2
• Substitute
• Answer:
Page 102 Problem 1
• A baseball has a mass of 0.15 kg is moving at a
speed of 40 m/s. What is the baseball’s
kinetic energy
• Given:
• Asked:
• Formula: KE = ½ mv2
• Substitute
• Answer:
Page 102 Problem 2
• A sprinter has a mass of 80.0 kg and a kinetic
energy of 4,000 J. What is the sprinter’s
speed?
• Given:
• Asked:
• Formula: KE = ½ mv2
• Substitute
• Answer:
Page 102 Problem 3
• A car with a mass of 1,500 kg doubles its
speed from 50 km/hr to 100 km/hr. By how
many times does the kinetic energy of the car
increase?
• Given:
• Asked:
• Formula: KE = ½ mv2
• Substitute
• Answer:
Potential Energy
Energy that is stored (available to do work)
• Examples
–Elastic potential energy – stored in a spring
–Chemical potential energy – stored in a
battery
–Gravitational potential energy- stored by
an object due to its position above the
Earth’s surface
Gravitational Potential energy
• The energy we store in an object when we lift it
above the earth.
• GPE is equal to the work we do in lifting an object
• work= Force x distance= Fg x h
• work = weight times the height
• Since Fg = mg and height is the distance moved
• GPE = work done= mass x g x height
• GPE= mgh
kg x m/s2 x m = kg m2/s2
Practice Problems- Potential Energy
Page 104: 1,2,3, 4EC
• What is the gravitational potential energy of a
ceiling fan that has a mass of 7.0 kg and is 4.0 m
above the ground?
• Given:
• Asked:
• Formula: GPE = mgh
• Substitute:
• Answer:
Page 104 Problem 1
• Find the GPE of a coffee mug with a mass of
0.3 kg that is on a counter top 1m above the
ground.
• Given:
• Asked:
• Formula: GPE = mgh
• Substitute:
• Answer:
Page 104 Problem 2
• How high above the ground is a baseball with
a mass of 0.15 kg and GPE of 73.5 J?
• Given:
• Asked:
• Formula: GPE = mgh
• Substitute:
• Answer:
Page 104 Problem 3
• A rock climber is 200m above the ground and
has a GPE of 117,600 J. What is the rock
climber’s mass?
• Given:
• Asked:
• Formula: GPE = mgh
• Substitute:
• Answer:
Page 104 Problem 4
• Suppose the mass of an object and it’s height
above the ground both were doubled. How
much would the object’s GPE change?
• Given:
• Asked:
• Formula: GPE = mgh
• Substitute:
• Answer:
Different Types of Energy
• Mechanical
• Kinetic Energy- due to motion
• Gravitational Potential Energy- due to position
• Electrical
• Chemical
• Sound
• Light
• Thermal (heat)
• Nuclear
Changes in Gravitational Potential
Energy (page 105)
2 meters
2 meters
2 meters
2 meters
2 meters
Conservation of Energy
Section 4:2 Page 107
Energy Transformation (P107)
Light Bulb
• Purpose is to convert electrical energy to light
energy
• But, also bulb gets hot so we know that some
of the energy has been converted to thermal
energy (heat)
• Heat is wasted because the purpose is light
• Fluorescent bulbs produce less heat so they
are more efficient.
• What are some other devices that convert
electrical energy to some other form?
Energy Conversion
• Chemical Energy to Mechanical Energy
– Burn gasoline in a car to make it go
• Chemical Energy to Electrical Energy
– A battery supplies power to a cell phone
•
•
•
•
•
Electrical Energy to Light Energy - ?
Electrical Energy to Sound Energy - ?
Electrical Energy to Mechanical Energy-?
Chemical energy to Thermal Energy
Electrical Energy to Thermal Energy
Chemical to Heat to Mechanical
Automobile Piston
• Gas fumes and air are combined under
pressure.
• Spark from the plug ignites the fuel/air
mixture.
• Explosion exerts pressure pushing the piston
back down.
• Changes chemical energy to heat energy to
mechanical energy.
• A lot of energy is lost to heat so we have a
cooling system to remove this heat.
Conservation of
Mechanical Energy
• Kinetic Energy is energy due to motion of an object.
KE = ½ m v2
• Potential energy is the energy due to position above
the earth.
PE = mgh
• Total Mechanical energy = KE + PE – wasted energy
Energy of a Projectile
• Thrown (or hit) horizontally
• Thrown (or hit) straight up
• Thrown (or hit) up at an angle
Read Page 110
Cursive Writing
• I hereby agree to the conditions set forth in
the test regulations and certify that I am the
person whose name, address, and signature
appear on the answer sheet.
• Name
Swing Energy (P110)
PE = maximum
KE = 0
PE = maximum
KE = 0
PE = minimum
KE = maximum
BUT
• Will a swing swing forever?
Law of Conservation of Energy
• Energy cannot be created or destroyed.
• Energy changes form but is not created or
destroyed.
• Total amount of energy in the universe does
not change.
• We can add energy or take away energy from
a small part of the universe.
• Energy in = energy out
– Hair Dryer (P111)
Swing Energy (P110)
GPE = maximum
KE = 0
TME= GPE+KE
GPE = ?
KE = 0
mass = 2 kg
14 meters
TME= GPE+KE
GPE = ?
KE =
2 meters
Ground
Useless Energy
• As the swing moves, air resistance and friction
convert some of the kinetic energy into
thermal energy.
• The loss of thermal energy causes the swing to
gradually slow down and stop.
Nuclear Energy (page 113)
• Prior to Einstein there were two separate laws
– Conservation of Energy
– Conservation of Mass
• Einstein E= mc2
Mass can be converted to energy and energy
can be converted to mass
Nuclear Fission
Nuclear Fusion
Fission (splitting)
energy
1
n
0
38
Kr93
1
n
0
235
U
92
1
n
0
54Xe
140
1
n
0
Fusion (joining)
2
H
1
3
H
1
3
He
2
Chapter 4 Assignments
– Page 102: 1-2-3
– Page 104: 1-2-3-4EC
– Practice Problem Handout
– Pendulum Lab- Monday 10/21
– Note Taking Work Sheet Tue 10/22
– Chapter 4 Review: 1-12, 22-25 Wed 10/23
– Chapter 4 Test Thursday 10/24
Practice Problems
• Find the kinetic energy of a ball with a mass of
0.75 kg moving with a speed of 50 m/s?
• Find the gravitational potential energy of a 80 kg
diver on top of a 10m high diving tower?
• If the diver jumps off the tower, what is the GPE of
the diver half way down to the water?
• If the diver’s kinetic energy is 3920 Joules when he
is half way down, what is his velocity?
• What will be the velocity of the diver just as he
hits the water? HINT: What will h = ?
Practice Problem 1
Find the kinetic energy of a ball with a mass of
0.75 kg moving with a speed of 50 m/s?
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Given:
Asked:
Formula:
Substitute:
Answer
Practice Problem 2
Find the gravitational potential energy of a 80
kg diver on top of a 10m high diving tower?
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Given:
Asked:
Formula:
Substitute:
Answer
Practice Problem 3
If the diver jumps off the tower, what is the GPE
of the diver half way down to the water?
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•
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•
•
Given:
Asked:
Formula:
Substitute:
Answer
Practice Problem 4
If the diver’s kinetic energy is 3920 Joules when
he is half way down, what is his velocity?
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•
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•
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Given:
Asked:
units
Formula:
Substitute
Answer with units:
Problem 5
• What will be the velocity of the diver just as
he hits the water? HINT: What will h = ?
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•
•
•
•
Given:
Asked:
units
Formula:
Substitute
Answer with units:
Chapter 4 Assignments
• Clear Desks except for calculator and Reference
Sheet
• Write this formula on your Reference Sheet
Total Mechanical Energy = KE + GPE
• Turn in homework before you leave
– Page 102: 1-2-3
– Page 104: 1-2-3-4EC
– Practice Problem Handout
– Pendulum Lab
– Note Taking Work Sheet
– Chapter 4 Review: 1-12, 22-25
Problems
• Given:
• Asked:
Units
• Formula: KE = 1/2mv2 , GPE= mgh, TME=KE+PE
• Substitute:
• Answer: