### Conservation of Energy

```Conservation of Energy
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Conservation of Energy
Introduction
Journals and Snapshots
The Snapshot button is used to capture the
screen.
The Journal is where snapshots are stored
and viewed.
The Share button is used to export
or print your journal to turn in your
work.
Each page of this lab that
contains the symbol
should be inserted into your
journal. After completing a
lab page with the snapshot
symbol, tap
(in the upper
right corner) to insert the
Note: You may want to take a
snapshot of the first page of
this lab as a cover page for
Conservation of Energy
Lab Challenge
How does the energy of a cart poised at
the top of a hill compare to its energy at
the bottom of the hill?
Conservation of Energy
Background
Gravitational Potential Energy, or energy of
position, is defined by the equation:
GPE = mgh
For an object on earth, the mass m and the
acceleration due to gravity g, remain
constant. Hence, only the change in height h
influences any change in Gravitational
Potential Energy GPE.
Conservation of Energy
...Background
For kinetic energy, or energy of motion,
the equation is:
1
KE =
mv2
2
For this same object of constant mass,
any change in the kinetic energy KE is
due to a change in velocity v.
Conservation of Energy
...Background
For a closed system the Total Energy TE is
defined to be the sum of the different types
of energy:
TE = KE + GPE + Heat + Light + …
We will create our own closed system, and
limit the forms of energy changing to Kinetic
and Gravitational Potential to observe how
they change, and how they relate to the
Total Energy of the system.
TE = KE + GPE
Conservation of Energy
Materials and Equipment
Collect all of these materials
before beginning the lab
• Motion Sensor
• Cart with Plunger
• Angle Indicator
• Track Bumper
• Rod Clamp
• Dynamics Track
• Rod Stand
• Balance (1 per class)
Conservation of Energy
Sequencing Challenge
A. From your
graph determine
the distance d
travelled by the
cart.
B. Connect the
track to the rod
stand using the rod
clamp.
C. Use distance d
travelled and angle
of track θ to find
the maximum
height h that the
cart travelled.
D. Begin collecting
data, then tap the
release button
launch the cart.
The steps to the left are part
of the procedure for this lab
activity. They are not in the
right order. Determine the
correct sequence of the
steps, then take a snapshot
Conservation of Energy
Setup
1. Attach the End Stop to one end of the Dynamics
Track then use the rod clamp to attach the opposite
end of the track to the rod stand.
2. Attach the Motion Sensor to the inclined end of the
track with the face of the sensor pointed toward the
end stop
3. Make certain that the switch on the top of the
motion sensor is set to the cart icon:
Note: It is best to have the Rod Stand positioned
next to the Motion Sensor so that it does not
interfere with the sensor.
Conservation of Energy
Setup
4. Mount the angle indicator to the side of the
track as close to the motion sensor as possible.
5. Connect the Motion Sensor to the SPARK
Science Learning System.
6. Use a balance to measure the mass of your cart,
then record that value in kg in the text box to
the right.
7. Place the cart with the plunger extended on the
track against the end stop.
Record the mass of your
cart in the text box below
then take a snapshot of this
page.
Conservation of Energy
Setup
8. Tap
to begin data collection. After a few
seconds tap
to stop data collection.
9. Record the initial position of the cart relative to the
Motion Sensor from the digits display into the text
box to the right, and then take a snapshot of this
page.
Conservation of Energy
Setup
Q1: Why is the cart set in position with the plunger
extended?
a) To determine the length of the plunger.
b) To determine if the cart is existential.
c) To determine the point of maximum spring
compression.
d) To determine the point where the plunger is no
longer influencing the motion of the cart.
then take a snapshot of this
page.
Conservation of Energy
Setup
8. Press the plunger on the dynamics cart all the way
into the cart until it locks in place.
9. Place the cart at the bottom of the track, resting
the plunger end of the cart against the fixed end
stop.
10.Tap the plunger release trigger on the top of the
cart launching the cart up the track.
Note: The plunger release trigger is found on the top
of the plunger-end of th`e cart.
11.Observe how far up the track the cart travels.
12.Adjust the angle θ of the track such that the cart
does not get closer than 15 cm to the Motion
Sensor when launched.
Once you have settled on a
suitable track incline angle,
record the angle θ in the box
below, then take a snapshot
Conservation of Energy
Collect Data
1. Press the plunger all the
way into the cart until it
locks in place.
2. Set the cart at the
bottom of the track.
3. Tap
to begin data
collection.
4. Tap the plunger release
trigger launching the cart
up the track.
5. Let the cart bounce once
or twice, then tap
to
stop data collection.
Conservation of Energy
Analysis
1. Use graph tools to find the
distance d between where
the cart left the bumper to
the cart's closest point to
the Motion Sensor.
* To Find the Difference
Between Two Data Points:
1. Tap
to open the tools
palette.
2. Tap
and then tap two
points on the data run.
and then tap .
4. Tap
to display the
differences.
Conservation of Energy
Analysis
2. Use the distance d travelled and the angle of the
track θ to calculate the maximum height h that the
cart travelled.
3. Use h, the acceleration due to gravity g (9.8 m/s2),
and the mass of the cart m to calculate the GPE of
the system with the cart at the top of the track.
GPE = mgh
Once you have calculated the
maximum height h and the
potential energy GPE of the
system, record them below,
and then take a snapshot of
Conservation of Energy
Analysis
4. Use graph tools to
determine the initial
velocity v of the cart when
the cart left the bumper.
* To Find the X- and Y-Values
of a Data Point:
1. Tap
to open the tools
palette.
2. Tap
and then tap a data
point.
3. Tap or to select
nearby data points.
Conservation of Energy
Analysis
1. Given that the cart momentarily comes to a complete stop before rolling back
down the track, what is the Kinetic Energy of the system at this point? Why?
Conservation of Energy
Analysis
5. Use the initial velocity of the cart v and the mass
of the cart m to calculate the kinetic energy of
the system with the cart at the bottom of the
track.
1
KE =
mv2
2
Once you have calculated the
KE of the system, record that
value as well as your value
for v in the text box below.
Conservation of Energy
Analysis
2. If the point at which the cart leaves the bumper is the lowest point of the
system, what is the Gravitational Potential Energy of the system at this
point? Why?
Conservation of Energy
Analysis
6. Use graph tools to help
determine the GPE of the
system at a third point in
time before the first
bounce. Enter the
calculated GPE value in the
text box below.
Conservation of Energy
Analysis
7. Use graph tools to help
determine the KE of the
system at the same point in
time on the curve. Enter
the calculated KE value in
the text box below.
Conservation of Energy
Analysis
3. Using your calculated values from the previous two pages, calculate the total
energy of the system at the third point in time. How does the total energy of
the system compare at the three different points in time that you investigated?
Conservation of Energy
Analysis
4. At what point in the cart's path was the Kinetic Energy of the system greatest?
Where did that original energy come from?
Conservation of Energy
Analysis
5. In observing the motion of the cart, the second and third bounce of the cart were
lower than the first, indicating less energy. Where did the energy go? In what form
was it when it was lost?
Conservation of Energy
Synthesis
1. An archer's bow can store 80 J of energy when drawn. If all that energy is
converted to Kinetic Energy when the arrow is released, how fast is the 0.1 kg
arrow traveling when it leaves the bow?
Conservation of Energy
Multiple Choice Question
1. How much Gravitational Potential Energy does a 4
kg jug of milk, set on the edge of a counter
1.2 m above the ground have?
a) 47.1 J
b) 471 J
c) 0 J
d) There is not enough information to draw a
conclusion.
then take a snapshot of this
page.
Conservation of Energy
Multiple Choice Question
2. A bobsled and rider have 100 kg of mass
combined. They come off a hill at 72 kph.
Assuming all of their Gravitational Potential Energy
was converted to Kinetic Energy, how high was the
hill?
a) 204 m
b) 42
c) 20.4 m
d) 264.2 m
then take a snapshot of this
page.
Conservation of Energy
Multiple Choice Question
3. A giant pendulum swings up to a height of 10
meters above the floor. When it reaches the
bottom of its swing it is traveling at 14 m/s. What
is the mass of the pendulum?
a) 1000 kg
b) 100 kg
c) 9.81 kg
d) There is not enough information to draw a
conclusion.
then take a snapshot of this
page.
Conservation of Energy
Congratulations!
You have completed the lab.