Download Kinetic Energy

Goals
Relate transformations and flow of energy
within a system-chemical, mechanical,
electromagnetic, light, sound, thermal,
electrical, and nuclear.
Identify energy transformations within a system
(e.g. lighting of a match).
1
Sound
THE ABILITY TO CAUSE CHANGE
Unit for Energy
• The Joule (J) is the SI unit
of Energy.
• And is defined as a force of
one newton is applied over a
displacement of one meter
• 1J= 1N●m
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
What types of energy are seen
here?
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
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.
6
Calculating Kinetic Energy
A formula to find
the kinetic energy
of any body
based on its
velocity.
The Unit for Kinetic Energy is
the Joule
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
Page 2
#’s 1-7
Don’t do #5
1. What is the kinetic energy of a 55 kg
object moving at 13 m/sec?
2. A 6 kg rock is thrown with a velocity
of 20 m/sec. What is the kinetic energy
of the rock?
m=
m=
v=
v=
KE =
KE =
3. When a golf ball is hit, it travels at 41
meters per second. The mass of a golf
ball is 0.045 kg. What is the kinetic
energy of the golf ball?
4. A ball has 475 J of energy while in
motion. If the ball is moving at 30
m/sec, what is the mass of the ball?
m=
m=
v=
v=
KE =
KE =
6. Susie Maroney from Australia set a
women’s record in long-distance
swimming by swimming 93.625 m in
24.00 h. If Maroney’s mass was 55 kg,
what was her kinetic energy?(Assume
her velocity is equal to her average
speed)
m=
v=
KE =
7. In 1994, Leroy Burrell of the United
States set what was then a new world
record for the men’s 100 m run. He ran
the 100 m distance in 9.85 s. Assuming
that he ran with a constant speed equal
to his average speed, and his kinetic
energy was 3400 J, what was Burrell’s
mass?
m=
v=
KE =
An object has a kinetic energy of
88 J and a mass of 45 kg , how
fast is the object moving?
m=
An object has a kinetic energy of
14 J and a mass of 17 kg , how
fast is the object moving?
m=
v=
v=
KE =
KE =
Potential Energy
• An
object
can store
energy
as the
result of
its
position.
7
Potential and Kinetic Energy
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
10
Calculating Gravitational
Potential Energy
Elastic Potential
• Elastic PE is
the energy
stored in
elastic
materials as
the result of
their
stretching or
compressing.
11
Practice Problems
Page 2
#’s 8-15
8. A man lifts a box with a mass of 13kg 9. What is the coaster’s potential energy
to a height of 12m. What is the potential at position “A”?
energy of the box?
m=
m=
g=
g=
h=
h=
GPE =
GPE =
h=
11. Ms. Andrews’s cat, Monkey, who has
a mass of 6.4 kg, has climbed on top of
the house to bird watch. If the house is
6.0 m tall, what is Monkey’s potential
energy?
m=
GPE =
g=
10. What is the cup’s potential energy?
m=
g=
h=
GPE =
12. A cart at the top of a 300 m hill has a
mass of 40 kg. What is the cart’s
gravitational potential energy?
m=
13. A boulder has 6000 J of potential
energy while sitting on top of a cliff. If
the cliff is 210 m above the ground, what
is the mass of the boulder?
m=
g=
g=
h=
h=
GPE =
GPE =
14. An apple in a tree has a gravitational
potential energy of 175 J and a mass of
0.36 g. How high from the ground is the
apple?
m=
g=
15. A 50 N object is lifted to a height of 3
meters. What is the potential energy of
this object? (hint: remember that
Newtons is weight…compare the
formula for weight and the formula for
GPE)
W=
h=
h=
GPE =
GPE =
12
13
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)
14
ENERGY BEFORE = ENERGY AFTER
Energy can be changed from one
form to another, but it does not
disappear.
15
Conservation of Energy
16
Conservation of Energy
TOTAL ENERGY OF THE SYSTEM REMAINS THE
SAME
Tutor Vista Activity
(click)
17
Conservation of Energy
KEi + PEi = KEf + PEf
TOTAL ENERGY OF THE SYSTEM REMAINS THE
SAME
18
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
19
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.
20
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
22
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.
26
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