Download Conservation Energy Lab

Conservation of Energy
Students will use well known physics principles to estimate the behavior of a
system. The ability to construct approximate theories is a foundation of science
and technology.
In most situations, an approximation is all that is possible. We must
understand that the approximations made to derive the formulas are to ensure
that the results accurately predict performance.
Conservation of Energy means that you cannot create nor destroy energy it is
said to be transformed. So, the sum of the kinetic and potential energy
everywhere is the same and that the total energy of an object remains
constant.
As the potential energy is increased by an increase in its height above the
earth, the kinetic energy is decreasing due to the object slowing down.
The tendency of an object to conserve its mechanical energy is observed
whenever external forces are not doing any overall work.
TEKS 5D: Conservation of Energy by Inquiry
Demo/ Engage Activity
The purpose of this experiment is to measure the potential energy and the
kinetic energy of a mechanical system and to quantitatively compare the two
forms of mechanical energy to determine if the total mechanical energy is
conserved.
We will investigate the law of conservation of energy and that the total
energy of an object remains constant. At every point in the motion of the
pendulum the total mechanical energy is conserved.
Set up: Obtain a stand, rollercoaster, CPO timer, photogate and a marble
1. Attach the roller coaster to the 5th hole in the physics stand.
2. Use the starting peg to start marble in the same place each time you roll it
down.
3. Make sure the marble stays on the tracks. It takes a couple of times to try
to keep it on the tracks.
Predict which location you think the marble will travel through the fastest
position (1,2,3,4,5,6 or 7)? Explain why?
Scenario #1: Calculate the speed and height at different locations on the
roller coaster. The speed of the marble is its diameter (1.9 cm) divided by the
time the photogate A. In order to get the height, you need to measure from
the table to the center of the hole for the light beam.
1. To measure the speed of the marble, attach a photogate so that the marble
breaks the light beam as it rolls through.
2. Plug the photogate into input A of the timer and use interval mode.
3. Be sure that the bottom of the photogate is flat against the bottom of the
roller coaster. If the photogate is not attached properly, the light beam will
not cross the center of the marble and the speed you calculate will not be
accurate.
Collect data:
Position
Height
Time,
Photogate A
(sec)
Distance
traveled
(cm)
Position 1
(5 cm)
1.9 cm
Position 2
(20 cm)
1.9 cm
Position 3
(40 cm)
1.9 cm
Position 4
(65 cm)
1.9 cm
Position 5
(85 cm)
1.9 cm
Position 6
(105 cm)
1.9 cm
Position 7
(125 cm)
1.9 cm
Speed
of marble
(cm/sec)
Drawing Conclusions
Question 1
If your speed looks similar to the graph above, what conclusion can be made
about the speed of the marble as it goes up?
Question 2: Looking at your data and the graph above how is the height of
the marble related to the speed of the marble?
Scenario #2:
1. Find the mass of the object – place the petri dish on the digital scale and
place it on the scale, now put the marble in the petri dish and record the
mass in grams
2. Calculate the Potential Energy – formula PE = mass x gravity x height
(Note: gravity = 9.8 m/s2)
3. Calculate the Kinetic Energy –formula – KE = mv2 / 2
4. Find the total Mechanical energy – formula – PE + KE = Total Energy
Position
Height
(cm)
Position
1
(5 cm)
35.5 cm
Position
2
(20 cm)
Position
3
(40 cm)
Position
4
(65 cm)
Position
5
(85 cm)
Position
6
(105 cm)
Position
7
(125 cm)
Speed
of marble
(cm/sec)
Mass of the
marble
(grams)
Gravitational
Potential
Energy
(Joules)
Kinetic
Energy
(Joules)
Total
Mechanical
Energy
(Joules)
Name ________________________ Period __________ Date __________
Post-Lab QUIZ
1. A pendulum swings as shown in the diagram. At which position is the kinetic
energy of the pendulum bob the least?
A.
B.
C.
D.
a
b
c
d
2. At which location is the speed the greatest? ________________________
3. Fill-in the 5 empty spaces below.