AP Physics Lab Guide
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Labs consist of 40% of your grade
You will usually have 2-3 labs per quarter
Sometimes labs will be repeated using a different procedure to increase accuracy
A lab group consists of 3-4 people, unless it is a partner lab
Lab reports usually have to be typed
Each person is responsible for writing their own lab report (you cannot turn in one for the whole
group) unless otherwise stated
Each Lab Report must have the following components:
1) Cover Page- The cover page must have the title of the lab, the date, and your name on it. Your
lab partners’ names must be in parentheses underneath your name as well
2) Abstract- The abstract must give a basic overview of the lab. It must briefly explain what the
experiment is designed to do and how you did it (not in great detail, though). A basic summary
of your findings must also be included. The abstract should not be more than one paragraph
long
A example of an abstract
This experiment is designed to prove whether or not momentum is
conserved in explosions. The experiment was conducted with a
frictionless track, two frictionless carts, and two photogates. Two mass
scenarios were used for the explosion portion of the lab. Mass scenario
one consisted of cart 1 having a mass of .50641 kg and cart 2 having a
mass of .50613 kg. Mass scenario two consisted of cart 1 having a mass
of 1.01042 kg and cart 2 having a mass of .50613 kg. These different
mass scenarios are intended to prove that momentum is conserved no
matter what the combination of masses of the carts is. For the
explosion portion of the lab, the initial momentum was 0 kgm/s for
both masses because they were both stationary. The lab proved that
mass was conserved in both mass scenarios of the explosion portion of
the lab because in both scenarios, final momentum was also 0 kgm/s.
This is because the carts’ momentums were in opposite directions and
cancelled each other out.
C example of an abstract
This experiment was designed to show whether or not
momentum was conserved. After running the carts on a
frictionless track, it was decided that momentum was
actually conserved. We conducted explosions. We used carts
of different masses. For the most part, the lab showed that
momentum was conserved.
3) Introduction- The introduction must state what the intention of the lab is. This should be a very
short paragraph.
A+ Example of an Intro
This lab was designed to show that momentum is conserved in
explosions. This entire lab was driven by the theory that, in a
closed system, momentum of the system before would be
equal to the momentum after an explosion. The explosions in
C Example of an Intro
This lab was intended to show whether or not
momentum is conserved.
this lab were perfectly inelastic. The momentum equation
used in this lab was P = mv. This lab was thus designed to show
that the momentum of the entire system before the explosion
was in fact equal to the momentum of the system after, thus
proving the law of conservation of momentum.
4) Procedure- The procedure must be written in paragraph form. It must be a very detailed
account of how you completed the lab. It must include the equipment that you used and how
you used it. You should also include which units everything will be measured in. This should be
approximately a paragraph long and should include enough detail that someone should be able
to complete the lab exactly how you did.
A+ Example of a Procedure
Two carts were placed on a frictionless track. The way the
carts are made allows one to attach them together by
magnets. There is also a small button on top of one of the
carts. Upon pressing the button, a small piece of metal
protrudes from one of the carts at the point where they
are attached. This button was effectively an “explosion
button” because pressing it would cause the two carts to
be propelled in opposite directions. Initial momentum was
known because the carts started at rest and were stuck
together. Thus, initial momentum was zero kgm/s because
the velocity of the initial system was zero. Two photogates
were placed on the frictionless track at an equal distance
from the origin (where the carts were initially at rest).
These photogates were used to help calculate the velocity
of both carts after the explosion occurred. The photogates
measured the time it took an index card that protruded
from the top of each cart to pass through the gate. Since
photogates were placed at both ends of the track, it is
possible to calculate the final velocity for both carts. The
final velocity can be calculated by dividing the length of
the card by the time it took that card to pass through its
respective photogate. Each card was the same length on
each cart in order to maintain some consistency. Three
trials were conducted with just the mass of the carts
themselves. In order to be more thorough, a second set of
trials was conducted with an additional mass added to one
of the carts (see “results” below for specific mass
scenarios). Also, it is important to note that the carts
moved in opposite directions after the explosion occurred,
meaning that one velocity must be considered negative in
calculating final momentum.
C Example of a Procedure
Two carts were stuck on a frictionless track. Then an
explosion occurred between the two carts and they went in
opposite directions. The carts were at rest initially, but after
the explosion they weren’t. A photogate was used to
measure how long it took the carts to travel to the
photogate. This was later used to calculate velocity.
5) Results- This section should include all data tables that you have. Data tables should include all
data collected and the units should be accurate. This section should also include any necessary
explanations required to fully understand what data was collected. This section should not just
be filled with data tables, but should also include the occasional sentence or two of explanation
(ex: if the initial velocity of a cart is zero, you should explain that that’s because all trials started
at rest). This section is also intended to have all calculations needed. There should be one
sample calculation for each calculation you completed. Sample calculations should show all
steps in the calculation and should include units at all points (not just in the final answer). There
should also be a table that includes all your calculated data as well. This section can be very
lengthy if the lab required numerous calculations, or it can be short if the lab wasn’t too
calculation-heavy.
A+ Example of a Results Section
Collected Explosion Data
Total Mass
Time for Cart 1 to Pass Through Photogate 1
Cart 1
Trial 1
Trial 2
Trial 3
Average
.22786 s
.23327 s
.25945 s
.24019 s
.51976 s
.43419 s
.51599 s
.48665 s
Total Mass
Cart 2
Time for Cart 2 to Pass Through Photogate 2
Trial 1
.32828 s
.21952 s
Trial 2
.27533 s
.22365 s
Trial 3
.26732 s
.22499 s
Average
.29031 s
.22272 s
Explosion Velocity Sample Calculation:
It should be noted that since the carts started at rest, their initial velocity is zero m/s. The carts final velocities (as an average) can be calculated by
dividing the length of the index card (which was .126 m long) by the time it took that card to travel through the photo gate. The sample calculation
below is for the final velocity of Cart 1 with its first mass scenario (no added weight). Also, Cart 2’s velocity is in the negative direction because it
travels in a direction opposite to that of Cart 1.
𝑣𝑓 =
.126 𝑚
.24019 𝑠
= .52459 𝑚/𝑠
Explosion Velocity Calculation Table:
Cart
Cart 1 (initial mass scenario)
Cart 2 (initial mass scenario)
Cart 1 (second mass scenario)
Cart 2 (second mass scenario)
Initial
Velocity
0 m/s
0 m/s
0 m/s
0 m/s
Final Velocity
.52459 m/s
-.43402 m/s
.25891 m/s
-.56557 m/s
*it should be noted that the term “initial mass
scenario” means the first three trials of each cart
before the masses were changed. Initial mass
scenario means the trials in which mass of cart 1
= .50641 kg and the mass of cart 2 =.50613 kg.
Second mass scenario means when the mass of
cart 1 = 1.01042 kg and the mass of cart 2
remains unchanged.
Explosion Momentum Sample Calculation:
The formula used for all momentum calculations is p=mv, where p is momentum, m is mass of the object (in kilograms) and v is velocity (in m/s).
Momentum calculations in this lab are designed to prove that momentum is in fact conserved. Thus, momentum of the system before and after the
explosion will be calculated. If momentum truly is conserved, then the momentum of the system before the explosion should equal the momentum
of the system after the explosion. The sample calculations below are for Mass scenario 1 (in which the mass of cart 1 was .50641 kg and the mass of
cart 2 was .50613 kg)
𝑚
𝑚
𝑘𝑔𝑚
𝑃𝑜 = (. 50641 𝑘𝑔) (0 ) + (. 50613 𝑘𝑔) (0 ) = 0
𝑠
𝑠
𝑠
𝑚
𝑚
𝑘𝑔𝑚
𝑃𝑓 = (. 50641 𝑘𝑔) (. 52459 ) + (. 50613) (−.43402 ) = 0
𝑠
𝑠
𝑠
Thus momentum is conserved because the momentum of the system before the explosion is equivalent to the momentum of the system after the
explosion.
Calculations for Mass Scenario 2 (in which cart 1 = 1.01042 kg and Cart 2= .50613 kg)
𝑚
𝑚
𝑘𝑔𝑚
) + (. 50613 𝑘𝑔) (0 ) = 0
𝑠
𝑠
𝑠
𝑚
𝑚
𝑘𝑔𝑚
𝑃𝑓 = (1.01042 𝑘𝑔) (. 25891 ) + (. 50613) (−.56557 ) = 0
𝑠
𝑠
𝑠
𝑃𝑜 = (1.01042 𝑘𝑔) (0
Summary Table:
Mass Scenario
1
2
Initial Momentum
0 kgm/s
0 kgm/s
Final Momentum
0 kgm/s
0 kgm/s
Momentum Conserved?
Yes
Yes
C Example of Results Section
Data:
Collected Explosion Data
Trial 1
.22786
.51976
Trial 2
.23327
.43419
Trial 3
.25945
.51599
Trial 1
.32828
.21952
Trial 2
.27533
.22365
Trial 3
.26732
.22499
calculation:
𝑣=
. 126
= .5
. 24019
calculation table:
Cart
Initial
Velocity
0
0
0
0
Cart 1
Cart 2
Cart 1
Cart 2
Final Velocity
.52
-.43
.25
-.56
Explosion Momentum Sample Calculation:
𝑃 = (. 50641 )(0) + (. 5)(0) = 0
𝑃 = (. 50641 )(. 52) + (. 506)(−.43) = 0
Momentum is clearly conserved.
6) Discussion and Conclusion- This is the final section of the lab and should be the place where you
wrap everything up. You should talk about your data; discuss any and all trends you discovered.
This is also where you should talk about errors. Errors can be classified as systematic or random,
and you should include possible solutions to correct this error. Overall, your discussion and
conclusion section should talk about whether your data supported what you were trying to find.
You should always include data in this section. If your data supports what you expected, make
sure you include a few examples of your data that support this (ex: if you thought that
momentum would be conserved and it was, include some data from a trial in which it was
clearly conserved). This section should be 1-2 paragraphs long and should be as detailed as you
can possibly make it.
A+ Example of Discussion and Conclusion
The explosion experiment proves that momentum is conserved during a
closed system of an explosion. In the first mass scenario (in which cart 1
had a mass of .50641 kg and cart 2 had a mass of .50613 kg), the
momentum before the explosion was 0 kgm/s. The momentum of the
system after the explosion was also 0 kgm/s. This is because the
explosion caused the two carts to travel in opposite directions. The two
carts’ momentums cancelled each other out because they were
travelling in opposite directions, thus resulting in a final momentum of
zero. This means that momentum was conserved. When an additional
weight was added to cart 1 (in the second mass scenario), momentum
was also conserved. The initial momentum of this explosion was zero,
because both carts started at rest. Again, the momentum after the
explosion ended up cancelling each other out. The cart with the larger
mass traveled with a smaller velocity. The cart with the smaller mass
traveled with a greater velocity. Thus, these equaled the same
momentum in opposite direction because the equation for momentum is
p=mv
Possible sources of error in this lab include the fact that the “frictionless”
tracks could not possibly be frictionless. The track that was used was
dusty (which is one of the more visible signs of friction present). Also, it’s
very hard to develop a truly frictionless surface. Although the track may
have been very smooth; it must have still possessed friction. This could
have skewed the data in a systematic manner, as it would cause the
velocities of the carts to be lower than their theoretical values.
Unfortunately, this is an error that cannot be feasibly solved, as perfectly
frictionless tracks do not exist. Another source of error was the fact that
two different photogates had to be used each time. It’s impossible to tell
whether or not each photogate had the same reaction timing. One may
have been less calibrated than the other. This would be a random error.
This error could be solved by using checking that both photogates are
equally sensitive by running controls through them and seeing if both
show the same time value. Another source of error in this lab would be
environmental conditions. There could have been randomly generated
gusts of winds from the air conditioning units. This would cause a
random error. The only solution to this error would be to conduct the lab
in a vacuum free of environmental errors. Unfortunately, this would be
impossible to do because the people conducting the experiments would
probably asphyxiate. Another source of error is air resistance. Air
resistance is not taken into account in these momentum calculations. Air
resistance would be a systematic error because it would cause the
velocities of the carts to be less than they theoretically should be. Again,
the only proper solution to this (other than calculating air resistance and
taking that into account) would be to conduct the experiment in a
vacuum.
C Example of Discussion and Conclusion
This experiment proved that momentum was conserved in
explosions. Momentum was the same before and after the
explosion. Different masses were used on the carts and
momentum was still conserved. See calculation section for
proof of this. We used p=mv.
There was probably some error in this lab. Sources of error
include human error and dust on the track. Human error
cannot be fixed. Another error was probably air resistance.
Overall this lab confirmed that momentum is conserved in
explosions.