Staple your papers
together in the upper
left-hand corner.
Include the lab number
and title.
Lab 2: Acceleration Due to Gravity
Don’t forget your
name, lab partners,
date, class, and section
number.
John Smith, with Steve Jones and Rob Brown
June 21, 2013
General Physics Lab I
Section 3
Purpose is clear and
concise, so we can
discuss the success of
the experiment later.
Additionally, the
purpose wasn’t copied
verbatim from the lab
manual.
Lab title is repeated.
Title: “Lab 2: Acceleration of Gravity”
Purpose:
Each section
of the lab is
labeled.
Boldface type
helps the
labels stand
out from the
text.
Measure the acceleration due to gravity of a freely falling body near the Earth’s
surface (g) using a Picket Fence and a Photogate.
Data and Calculations:
Below is a diagram of the apparatus for this experiment:
Picket
fence
A neatly handdrawn, labeled
diagram of the
apparatus is shown.
While not necessary
for our purposes, it
is a nice touch.
Qualitative observations
are reported.
The distance vs. time graphs are parabolic (see attached graph), and the velocity
vs. time graphs are linear.
The purpose of the following data is to determine the acceleration due to gravity
at the Earth’s surface.
Purpose of the table is
Tables are a quick and
clear way to show your
data.
Original data is shown.
*
Trial
1
2
3
4
5
6
2 *
C (m/s )
4.907
4.899
4.796
4.905
4.905
4.910
stated.
2 **
g (m/s )
9.814
9.798
9.592
9.810
9.810
9.820
Table heading has
appropriate units.
This is the data taken from the plot of distance vs. time. See attached graph for Trial 1.
This column was calculated from the data taken in the lab from the equation g = -2 C.
**
Discussion in this
section is limited
to how the data
was handled.
Save the rest of
the discussion for
the Conclusion.
Inspecting the data shows that Trial 3 is significantly lower than the other five
trials. We expect that the Picket Fence was tilted and fell through the Photogate at an
angle, resulting in a lower value of g (see the Conclusion section for more information).
Since that value is probably from an incorrectly performed trial, it has been rejected and
the rest of the calculations ignore it.
Sample
calculations
are shown and
clearly
indicated. The
rest of the
calculations
were done in
the lab
notebook.
Therefore, the minimum, average, and maximum values for the trials are:
2
Acceleration (m/s )
*
Average*
9.810 m/s2
Minimum
9.798 m/s2
Maximum
9.820 m/s2
The average was calculated from:
(9.814 m / s ) + (9.798 m / s ) + (9.810 m / s ) + (9.810 m / s ) + (9.820 m / s )
2
g=
Again, use tables.
g = 9.810 m / s
2
2
2
2
5
2
From the maximum, minimum and average values, we get our best answer and
uncertainty for the acceleration due to gravity:
Statements of
uncertainty are
shown in table
form.
Acceleration due to gravity (g)
Precision*
Percent Error**
(9.81 ± 0.01) m / s 2
0.1%
0.0%
*
The precision was calculated as follows:
0.01 m / s 2
Precision =
× 100% = 0.1%
9.81 m / s 2
**
The percent error was calculated as follows
(9.81 m / s 2 ) − (9.81 m / s 2 )
% error =
× 100% = 0.0%
9.81 m / s 2
Results:
Results and
Conclusion
measure the
success of the lab
based on the
Purpose section
above.
Sample
calculations
are shown and
clearly
indicated.
The Results section
briefly restates the
important results found in
the Data and Calculations
section. Figures of
uncertainty are included.
Arguably, this section
could be combined with
the Conclusion.
From the data taken for this experiment, we determined that the acceleration due
to gravity at the Earth’s surface is (9.81 ± 0.01)m/s2. The value was measured to a
precision of 0.1% and a percent error with the accepted value of 9.81 m/s2 of 0.0%.
Additionally, the accepted value lies within the uncertainty ± 0.01 m/s2 of the experiment.
Conclusion:
OOPS!! The
data didn’t come
out as expected!
The conclusion
discusses a
reasonable and
defensible way
that this mistake
was handled.
The acceleration of gravity measured in this lab verified that the accepted value of
g is 9.81 m/s2 to within the uncertainty of the experiment. Additionally, our
measurement was precise, with a small uncertainty of 0.01 m/s2.
In performing our calculations, it was noted the value of g in Trial 3 was
unusually low compared to the other values. This is probably because the Picket Fence
was dropped at an angle that increased the distance, and therefore the measured time,
between dark and transparent bands. This results in a lower calculated value of g for this
trial. Since Trial 3 was done incorrectly, we rejected the data from this trial and
calculated our final result from the other five trials.
This paragraph
correctly argues
why the result of
Trial 3 was
lower, rather than
higher, than
expected.
Questions posed
in the lab manual
are completely
and concisely
answered in a
few sentences in
the Conclusion.
There are two main sources of error in this experiment. First, there is air
resistance present in the measurement. Secondly, it is difficult to make certain the Picket
fence is dropped perfectly vertically every time. Both of these could contribute to the
uncertainty of the experiment. However, since the uncertainty was small, they cannot
have contributed much, except as explained for Trial 3.
The distance vs. time graphs are parabolic because the motion is uniformly
accelerated. Additionally, the velocity vs. time graphs are linear for the same reason.
For Trial 6, the Picket Fence was thrown downward, but let go before it entered
the Photogate. This does not change the acceleration, because the Picket Fence was still
only under the influence of gravity as it fell through the Photogate. Graphically, this is
because the slope of the velocity vs. time graph does not change, only the values on the
graph change.
The Conclusion, and the lab as a whole, is short and to
the point, but still manages to be complete. The phrase
“Economy of Words” should come to mind.
Sources of
error are
discussed.
Graphs can be attached to the end of the lab
report as appendices. If you want, you may
also include them in-line with the text of the
Data and Calculations section if your word
processor will let you.
Distance vs. Time for Picket Fence
Graphs should be a full page and should be clearly labeled.
Labels should include a title, x-variable and y-variable with
units in parenthesis, and scales on each axis.
0.4
0.35
y = 4.9070 x2 + 0.7776 x + 0.0002
0.3
Equation of best fit
line is displayed.
Distance (m)
0.25
0.2
0.15
0.1
0.05
0
0
0.05
0.1
0.15
Time (s)
0.2
0.25