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Prelab 0
Started: Aug 25 at 10:22pm
Quiz Instructions
This is the first Prelab Activity of the Semester. Complete the following. As long as you make
meaningful attempts at each question, you'll receive full credit. Make sure to check your results for
automatic feedback. Feel free to post any questions or comments to Chatter (https://
utexas.instructure.com/courses/1463030/external_tools/112085) !
Prelabs will be due before your lab starts, so that your TA can review results before labs begins.
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Question 1 0 pts
Welcome to the first Prelab Activity of PHY 105M!
As you'll see in your first lab this upcoming week, you'll often be given more freedom in how you
approach experiments in this class compared with what you might be traditionally used to.
Because of this it typically won't be necessary for you to write a full formal lab report afterwards since
we're more interested in how you chose to approach an experiment and an (organized) version of
your lab notes will be sufficient for this.
On the other hand this means you'll want to make the most of your time in lab, and therefore, that
you'll want to be as prepared for lab as possible. The Prelab Activities will probably be longer than
you're used to and require more meaningful thinking and planning. The idea is the more seriously you
take them, the better prepared you'll be for lab activities.
In short: plan on spending less time on formal lab writeups between labs, and more time on Prelab
Activities.
Got it
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Question 2 1 pts
Since this is the first Prelab Activity and the course is just getting going, let's make sure you've taken
some time to review the Course Intro Module (https://utexas.instructure.com/courses/1463030/pages/
course-overview-and-schedule?module_item_id=g0bb8a3b6c18593dfe6054d27d0d132ac) .
If you have any questions about the contents, please post to discussions or contact the instructional
team as explained in the module itself.
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Quick check to make sure you understand the schedule and syllabus: How many labs do we have
this semester (including Lab 0?)
9
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Question 3 1 pts
And what are you supposed to do if you know in you're going to have to miss a lab due to illness or
other unavoidable conflicts?
Let your TA know in advance, we will have a make up lab session
Let your TA know at the end of the semester and it'll be dropped
Do nothing
Call 911
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Question 4 0 pts
Most Prelab Activities will include a discussion of the necessary concepts and models from General
Physics I that we'll be investigating in lab that week. This week, to keep things simple, we'll introduce
the models within the lab itself and instead will focus introducing some foundational skills related to
measurement.
To start with, input your height.
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6� 4 inches
p
3 words
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Question 5 1 pts
In your answer to the previous question, you likely wrote something like:
5'8''
or
1.72 meters
etc.
Notice the following!
1) You (hopefully) used some reference unit, such as feet/inches or meters. Why? Because a number
on its own would've been unclear.
2) You gave a number which represents your height to the best of your knowledge.
3) You (likely) didn't write something like 5'8.125147'' or 1.7285326 meters. Why? Because you
probably don't know your height to that degree of precision (and in fact, your height can even change
a bit over the course a day). So in recording your answer you (implicitly) acknowledged some
uncertainty in your knowledge of your height.
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This is characteristic of all measurements: they include a best estimate, uncertainty, and reference
units. In this lab course we want you to write measurements this way:
[Best Estimate]+/-[Uncertainty] [Units]
For example a height might be:
1.72+/-.01 meters.
Note a final point:
4) The decimal precision of the best estimate and the uncertainty must match! It wouldn't make much
sense to report, say, 1.721543+/-.01 meters since the extra digits are uncertain.
Try inputting your height again below, this time following the guidelines given. Use whatever
uncertainty you believe to be appropriate.
6� 4 ich +/-.05inch
p
5 words
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Question 6 1 pts
Uncertainties can arise for all kinds of different reasons. We will see many examples over the course
of the semester.
There are two primary kinds of uncertainty we'll encounter in lab this week. One is the uncertainty due
to the limitations of a measuring device. Let's discuss how to handle this.
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Consider the reading below:
This is an "analog" device. How should we assign a best estimate and uncertainty? We do the
following:
1. To get a best estimate, judge the marking closest to the reading.
2. To get an uncertainty, we use 1/2 the smallest increment (this represents our rounding and reflects
the precision of the instrument).
It's important to note that measuring devices have inherent (systematic) uncertainty related to the
limitations of the device, not just to the limitations of the markings. In this class we will always assume
this uncertainty is less than or equal to the rounding uncertainty.
What would you report as a measurement from the speedometer?
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5.2 +/- .5 m/s
p
5 words
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Question 7 1 pts
What about a digital device, like a stopwatch? See the following:
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Unlike the analog device, we have no idea what the next digit might be. It could be 1:23.441 or
1:23.449. Because of this, for digital devices we'll use the convention that the uncertainty is a whole
value of the precision, not half. What would you report?
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1:23.44 +/-.01
min/S/ms
p
7 words
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Question 8 1 pts
So far we've discussed the uncertainty in a measuring device. But there is another kind of uncertainty
that comes from the fact that often when we repeat a measurement multiple times, we don't get the
same thing each time. For example, open this simulation
(https://www.justpark.com/creative/
reaction-time-test/) .
Try out the experiment a few times and record the results. Do you get the same thing each time,
within the uncertainty?
True
False
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Almost certainly not! Is this because the time measuring device in the simulation is broken? No.
There are just many random influences on your reaction time that vary with each trial. This introduces
a different kind of uncertainty. In this case it's much larger than the uncertainty of the measuring
device you're using.
We can think of things in terms of accuracy vs. precision:
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When we measure something with a meterstick multiple times, we typically get the same thing again
and again. This means we're likely in picture #1 or #2. Since we might be in #2 (the meterstick might
be a tad inaccurate) we use this as the uncertainty. When we measure our reaction time, we're
somewhere in #3 or #4. How can we deal with this?
Well, we can collect many data points and try to discern the "typical" value and the "spread" and use
these to determine uncertainties. Let's do this with your reaction time. We'll have you propose your
own answer on how to do this. There's no right answer we're looking for, think about it yourself. Just
follow the next few prompts.
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Return to the simulation and collect and record 20 data points. Put them in excel (or google sheets,
etc.) in a table, and make a histogram:
Highlight the data, click on insert, and select the histogram.
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Question 9 0 pts
Now do this a second time, but this time listening to music. Make a histogram. Take a look at the two
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of them. Do you notice any difference between the two distributions?
1. Determine which of the two reaction time cases tended to be longer vs. shorter, or say if they're
about the same.
2. Determine which of the two cases tended to be more spread out vs. less, or say if they're about the
same.
Edit
12pt
View
Insert
Format
Tools
Table
Paragraph
1. Listening to music is longer
2. Has more spread when listening to music
1
p
14 words
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Question 10 1 pts
Finally, come up with a procedure for assigning a single number "best estimate" and an associated
"uncertainty" for each case. By procedure we mean a formula (or else at least an algorithm) which
takes the data in and spits out a result. Explain what the procedure is and what you get in the two
cases.
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12pt
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View
Insert
Format
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Table
Paragraph
p
0 words
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Question 11 1 pts
One way to get the best estimate in the previous task is to take the average of the data. With enough
trials you will need faster way to calculate than just pen and paper, for this you can use Excel or
Google Sheets (we'll use Sheets in this example).
To use Google Sheets as a calculator all you have to do is include an = sign into a cell, as shown in
the gif below (note that it doesn't calculate without the = sign)
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The calculation doesn't have to involve only typing into a single cell. You can have data in multiple
cells and then add them by selecting each cell:
Sheets can also recognize and continue patterns that you make up. For example, in the gif below is
counting one by one. The first three cells are typed out and then highlighted. Once highlighted, just
drag the blue circle down as many rows as you like and Sheets will count:
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Got it?
Yes
No
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Question 12 1 pts
The previous two functions can be combined to speed up your calculations. For example, say you
have two columns of data and you want to add them line-by-line. This is easily done using the = sign
along with Sheets' ability to recognize patterns (by dragging the blue dot down):
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Note that Sheets has an auto-complete function. This isn't available on all spreadsheet software, but
feel free to use it if it is available to you.
Try it yourself: Open up Sheets or Excel and make two rows of data, then add them as shown
above. Upload a screenshot of the results
Upload
Choose a File
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Question 13 1 pts
Sheets also has built in functions that are very handy. Let's say you have a column of data that you
want sum. There exists a SUM function that can be used here. All it takes is to start with = and then
type 'sum' (using the Tab button to auto complete it if you want). Then just highlight all the cells you
want to sum:
sum.gif
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You can combine this function with other operations as well. For example, you can find the average
by dividing the sum by the number of cells you summing:
sumavg.gif
Try it yourself: In Sheets make a column of data and average them as shown. Upload a screenshot
of your results.
Upload
Choose a File
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Question 14 1 pts
There are many functions available in Sheets/Excel. A faster way to do averaging is to simply use the
built-in 'average' function:
avg.gif
Try it yourself: Use the 'average' function on the set of data you made in the previous question.
Upload a screenshot of your results
Upload
Choose a File
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That's it for today! You're TA will review your proposals and follow up in class with a discussion of how
to agree on a consensus approach.
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