Transcript Energy

1
THE ABILITY TO CAUSE CHANGE
Relate transformations and
flow of energy within a
Goals
system-chemical,
mechanical,
electromagnetic, light,
Identify energy
transformations sound, thermal, electrical,
within a system and nuclear.
(e.g. lighting of
a match).
Sound
2
mechanical energy
Types of Energy
Thermal energy - due to temperature
(recall that this comes from the motion
of molecules, so it is really kinetic
energy)
Heat energy -transfer of thermal energy
Chemical Potential Energy - stored in
chemical bonds
Nuclear energy - stored in the nuclei of
an atom
Electrical energy - EM interactions
3
1.
2.
3.
4.
5.
6. Radiant energy -carried by EM waves
4
Energy
• Energy is the capacity (ability) to
do work.
• Potential Energy: Present in an
object that has the potential to
move because of its position
• Kinetic Energy: Associated with an
object in motion
Potential and Kinetic Energy
Question
• An amusement park wants to build
a new roller coaster. They want
the 2nd hill to be 65m tall.
• How tall should they make they
make the 1st hill?
• What information do we still need?
5
Kinetic Energy
• Motion
• KE of an object
depends upon two
variables:
1. the mass (m) of the
object
2. the speed (v) of the
object.
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Calculating Kinetic Energy
A formula to find
the kinetic energy
of any body
based on its
velocity.
Unit for Energy
(add everything in blue to 1st page)
• The Joule (J) is the SI unit of Energy.
– The calorie is another common unit for energy
• Where does this come from?
2
(KE = ½ m v )
• 1J= 1N●m
Example Problems
Kinetic Energy (KE = ½ m v2)
1) The velocity of a
car is 65 m/s and its
mass is 2515 kg.
What is its KE?
2) If a 30 kg child
were running at a
rate of 9.9 m/s, what
is his KE?
Practice Problems
• IN THIS ORDER….
–Page 2: #s 6, 7, 8, 5
Potential Energy
• An
object
can store
energy
as the
result of
its
position.
7
Potential and Kinetic Energy
Click photo
8
Forms of potential energy
9
Gravitational Potential Energy
• GPE is the energy stored in
an object as the result of
its vertical position (i.e., height).
• Amt. of GPE is dependent on
two variables:
1.the mass
2.the height
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Calculating Gravitational
Potential Energy
Elastic Potential
• Elastic PE is
the energy
stored in
elastic
materials as
the result of
their
stretching or
compressing.
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12
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Conservation of Energy
Energy cannot be created
or destroyed…only
changed from one form
to another.
The total energy of an
isolated system
remains constant
(isolated systems have
no external forces and
no mass changes)
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ENERGY BEFORE = ENERGY AFTER
Energy can be changed from one
form to another, but it does not
disappear.
15
Conservation of Energy
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Conservation of Energy
TOTAL ENERGY OF THE SYSTEM REMAINS THE
SAME
Tutor Vista Activity
(click)
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Conservation of Energy
KEi + PEi = KEf + PEf
TOTAL ENERGY OF THE SYSTEM REMAINS THE
SAME
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Conservation of Mechanical Energy:
KEi + PEi = KEf + PEf
Problem: A student lifts his 2.0 kg pet rock 2.8 m
straight up. He then lets it drop to the ground.
Calculate the following:
1) How much Potential Energy does it have at the top (before he
drops it). 54.88 J
2) How much Kinetic Energy does it have Total=54.88
at the top (before he
54.88 = PEf + KEf
drops it).
0J
54.88 = mgh + KEf
3) After it is dropped, how
54.88 = (2) (9.8)(1.4) + Kef
much KE will it have when
54.88 =27.44 + KEf
it is 1.4 m above the ground?
27.44 J = KEf
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Conservation of Mechanical Energy:
• Conservation of ME only hold
true when the only energies
of the system are KE and PE.
• Therefore, in the presence of
friction energy is transformed
to other types of energies.
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Energy Conversion
When one type of energy is changed or
transformed into another type of energy
Tutor Vista Activity
(click)
2
1
Examples
Battery
Can you think of More?
ENERGY PROJECTS
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Energy Conversion
clip
23
What about a falling object?
What happens when it hits
the ground?
Where did the energy all go?
24 Energy Conversions of a dropped object
•As it is falling and when the object hits the ground the energy
is converted into other types of energy such as:
•sound energy (waves), Light Energy (sparks), thermal
energy due to friction (heat) in the ground and air,
vibrations in the earth (energy waves.)
•If the object bounces, some energy is converted
momentarily into elastic potential energy.
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EOCT Questions
Which statement about energy is true?
A Energy can be increased in a closed
system.
B Energy cannot be conserved.
C Energy can be decreased in a closed
system.
D Energy cannot be created nor destroyed.
Wile E Coyote & Roadrunner Clip