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How to write an IB Physics Lab Report
...write it to meet the IB requirements!
P(a)
P(b)
Dc
Dp
CE
Lab
Book
(DC)
Pa Pb Dp CE are a separate report with cover sheet
Italicized comments below refer to my evaluation of the lab
report presented here. This report does NOT represent a
“perfect report” For a more detailed P(a) see the file
0_0_IB_Pa_labs_Q1.pdf
Problem Statement:
What are the motion characteristics of a
“marble” launched thru a plastic tube?
This cannot just be
a re-statement of
the “aim” provided
by the teacher.
P(a) Hypothesis:
The motion characteristics of a
launched marble can be completely
described by studying the initial
horizontal launched velocity and the
resulting acceleration of the marble.
The height of the tube will affect the
exit (horizontal) velocity. The exit
velocity along with “g” = 9.81 m/s2 will
affect the motion characteristics.
 IB Lab Writing 802
1
Note how this
relates the
hypothesis (or
prediction) to the
research question
and discusses
some quantitative
expectations.
Variables:
What are the ‘constant’ or non changing
for each trial? (controlled)
What variable will be changed or
manipulated from trial to trial?
(independent)
- height of the tube (the varied or changed
variable)
- same marble
-same tube material
-same drop sequence and procedure
-same room temperature
“g” = 9.81 m/s2
...
Lets assume that for this experiment we
will keep all variables the same except for
the height of the tube and see how velocity
is affected.
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 IB Lab Writing 802
2
Note that you must
clearly articulate
what variables you
are interested in
and which ones
will remain
constant from one
trial to another.
You cannot change
more than one
variable at a time.
P(b) Method
Tubes of various lengths (height) will be
used. (tubes of the same material)
The same marble will be used in each run
A motion detector will be used to measure
the exit velocity
A cardboard launch mechanism will be
employed to ensure the marble is always
dropped in the ‘same way’.
tape measure
tubes of various heights
Appropriate
measuring tools
have been selected
here. A tape
measure and a
motion detector.
Keeping the same
marble and
employing the
cardboard launch
mechanism allow
for the control of
the variables.
A diagram is VERY
important in this
section!
Motion detector
A cardboard ‘shutter’
will be used to ensure
the marble is always
dropped the same
way in each trial.
The procedure is to set up the tube
assemble and shutter as shown, start up
the motion detector software, pull the
shutter to release the marble and then
analyze the motion detector graph to
determine the exit speed of the marble.
Repeat each drop 3 to five times at
various heights.
By repeating the
trials at various
heights sufficient
relevant data
should be
collected.
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 IB Lab Writing 802
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Dc
Labbook entry
Date: Oct 1, 2001
Note that this
particular section
(Dc) belongs in your
bound lab book!
Marble velocity lab
Data:
marble characteristics:
green snake eye, radius= 0.5 cm, mass = 45 grams
room temp: 22 ˚C ± 0.5 ˚C
Trial
1
2
3
4
5
Drop Height velocity
ave
(cm)
(cm/s)
20 ± 0.5
2.8 ± 0.1
20
2.9
20
2.7
20
2.6
20
2.8
2.7 ± 0.1
6
7
8
9
10
30
30
30
30
30
3.1
3.4
3.2
3.1
3.0
11
12
13
14
15
40
40
40
40
40
3.7
3.8
3.7
3.9
3.8
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3.2 ± 0.1
The raw data is in a
TABLE allowing for
easy interpretation.
3.7 ± 0.1
e
 IB Lab Writing 802
Both qualitative
(green snake eye
marble) and
quantitative data
(drop height and
velocity) are
recorded. The
measurement
uncertainty in the
drop height ( ± 0.5)
and exit velocity
(±0.1) are clearly
associated with the
measurement
including the correct
UNITS and
SIGNIFICANT DIGITS)
4
Recording data
without a table
almost guarantees
point loss!
D(p)
Drop Height
ave vel
cm ± .1
m/s
Ex
±
10.0
2.3 ± 0.1
20.0
2.7
30.0
3.2 ± 0.1
40.0
3.7
50.0
3.9
60.0
4.0 ± 0.1
am
p
For data
processing you
need to clearly
show how you
processed
calculated results
from the raw data.
Another table with
the raw and
processed data is
helpful.
le
Marble Velocity vs height
v
e
l
c
m
/
s
±
0
.
1
4.0
3.9
3.8
3.7
3.6
3.5
3.4
3.3
3.2
3.1
3.0
2.9
2.8
2.7
2.6
2.5
2.4
2.3
2.2
5.0
10.0
15.0
20.0
25.0
30.0 35.0 40.0
height (cm) ± 0.1
45.0
50.0
Graphs of data are the most common and easiest
method of presenting your results.
All graphs must be:
• titled
• axis labeled with units AND uncertainty
If appropriate, “error bars” indicating the uncertainty
in the graph.
For this graph the uncertainty in height ( ± 0.1 cm) is
nearly impossible to see on the graph but the error in
velocity is not. Hence an error bar of ±0.1 cm/s length
is indicated in the vertical.
In general, NEVER “connect the dots” on a graph. You
must perform some sort of regression analysis.
 IB Lab Writing 802
5
55.0
60.0
Conclusion and evaluation
As expected from the studies of
motion, as the drop height increases,
the horizontal exit velocity increases
as a NON LINEAR function, possibly
a square root function.
This conclusion
related the original
problem statement
and hypothesis to
the data processing
graph of a non
linear function.
v = 2 a ∆d
As a check on the validity of this
method for finding the velocity of the
marble as it exits the tube the following
was performed.
Using a simple horizontal launch setup
the predicted drop points were
compared to the actual measured drop
points.
A further
interpretation of
the results is
performed.
Sometimes it is
better to compare
your results with
accepted literature
values. In that
case you should
always compare
your results with
literature values to
find the error in
your value as
compared to the
accepted value.
predicted vs measured
height (cm)
predicted (cm)
measured (cm) % error
10
20
30
 IB Lab Writing 802
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Conclusion and evaluation continued:
The limitations and weaknesses in this lab
were:
• accurate method of measuring the
velocity: The motion detector could not
always “see” the small marble and missed
the velocity.
• consistent initial drop height: The drop
mechanism would sometimes “sag” letting
the marble drop from a slightly lower
height than the top of the tube.
• consistent tube height: The tubes would
not always fit together consistently.
• human error: The motion detector was
not always started soon enough to catch
the marble just as it exited the tube.
The procedure
needs to be
evaluated here
discussing (with
details) the
limitations,
weaknesses and/
or errors in the lab.
If your only error
mentioned is
“human” error you
get zero points in
this section.
Suggestions to improve this lab are:
Change the velocity detector alignment to
ensure it always see’s the marble or look
for a better detector.
Build a more rigid launch mechanism to
prevent sagging.
Use single piece tubes if available.
These
suggestions
MUST relate to
the weaknesses
or errors
described above.
Unrealistic or
simplistic
suggestions are
not acceptable.
Rewrite the procedure so that the detector
is turned on before the marble is launched.
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 IB Lab Writing 802
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