dropbox DROPBOX! Prepare to safely archive your data and prepare to share files with lab partners. See Archive Data link.

The string should be short enough that the mass system never touches the floor!
Each hanger costs $99.91. DON'T BREAK THEM.

It is very important that you mass each mass system before each run!

You should have the following configuration for trial one:
HANGER + 100g
(+ 8 High-Tech Washers for the rest of the trials.) With each trial after trial one, you should add one more washer to the system. 8 more washers, nine trials.
You must mass the hanger system for EACH RUN!


Please note: If the movie is too small,
please watch via youtube using the YOUTUBE button on bottom right of each video.
And, some videos have much higher quality. Find the HD version using the gear icon.
Rotational Inertia

Measurement Hints:



Number 6 of the post lab asks us to calculate the force of friction given the vertical intercept and a measurement for the bearings from the center of the wheel. Is the measurement for the bearings from the center of the wheel the diameter of the bearings or the radius?
Watkins, Stefanie
Mon. 08, Nov 2004, 21:57
Take the center of the big wheel, measure outward 2mm (for example.)
That is where the bearing contacts the wheel.
Yes, the bearing contacts the wheel at its opposite side and it rubs against another bearing, and on the inside, and...
Just take the simple case of one contact surface rubbing a given distance from the big wheel's center.
Tue. 09, Nov 2004, 07:16

Hi Douglas:
When we added a trendline to our torque vs. angular acceleration graph we ended up with a negative y-intercept. According to the torque equation in the manual, our y-intercept should be positive. Does this mean that something is wrong with our data? Thanks.
Fri. 18, Nov 2005, 14:28
Yes, that does mean something is wrong with the data. Simply make a note on your graph explaining this oddity as best you can. The best remedy would be to retake the data, and at least re-analyze the data; but time does not permit at this point.Douglas
Mon. 21, Nov 2005, 05:31

When we add the line representing I3 do you want us to add that data to our data sheets as well?
- Thanks
Sat. 26, Nov 2005, 11:41
Yes. There you should add an I3 column in the data sheet as well as a line on the plot.Douglas
Mon. 28, Nov 2005, 10:40

Would you refresh my memory on how to calculate the percent difference? Thanks
Tue. 13, Nov 2007, 16:28
|Diff| / Average *100%Douglas
Wed. 14, Nov 2007, 10:29

Question 6 in the post lab: "If the bearings are 2 [mm] from the center of the wheel,
then what is the force of friction?"
what does 2 mm stand for ?
Tue. 14, Jul 2009, 16:51
mm is millimeter.
2mm means the force is applied that far from the center.
Wed. 15, Jul 2009, 11:36

Since the lab is being postponed (winter weather), I assume the deadline for the prelab will also be moved?Anonymous
Wed. 28, Oct 2009, 19:13
Yes, the Pre and Post deadlines will be moved later today.
Thank you.
Thu. 29, Oct 2009, 05:07

how do I find the resolution of error for question #6Anonymous
Fri. 16, Apr 2010, 09:07
That is not a simple answer to give through email.
Here is one example:
Radius of Big Wheel = 0.10232 [m] ± 0.00002 [m] (Uncertainty is from resolution of large vernier caliper of 0.02 [mm])

Beware: each measurement is treated differently. Basically, ask these questions:
a) What was the resolution of my measuring device?
b) Could I use the device to that resolution or were there complications? (e.g. parallax)
c) The best question, when available: Can I take repetitive measurements and find a standard deviation?
Sat. 17, Apr 2010, 07:20

Hey Howie, I was wondering if our values for T1 (example: 5253.117 N*m) are correct because the slope of our graph is in the thousands.Anonymous
Thu. 11, Nov 2010, 19:24
5[kNm] is not likely for this experiment. Check values for Radius and dropping masses.
Radius should be around 0.1[m]. Dropping mass around 0.1[kg] more or less.
Fri. 12, Nov 2010, 04:21

Problem 6 of the post-lab is asking for the standard deviation of the acceleration, how do I calculate this, for in every other lab the data studio has calculation standard deviation for us?
Houck, Hannah
Sun. 14, Nov 2010, 14:46
During lab each student should discover uncertainties. If you didn't, then you may simply take the uncertainty in slope from your sample picture of V vs t from DataStudio for trial 1. The slope of V vs t is of course acceleration and an uncertainty in the slope is given next to the slope value.Douglas
Mon. 15, Nov 2010, 07:38

Hi Douglas,
On the post lab question #2, it asks for the units for angular acceleration (alpha) but does not give the option of radians per seconds^2. Is there some conversion for those units which I am unaware of? It seemed the only other options were for torque, Newtons, linear acceleration, velocity, etc.
Sat. 21, Jul 2012, 08:52
angular acceleration was defined as the ratio of linear acceleration to radius; dimensionally this ratio deduces to a per second squared. Radian is often suppressed when assumed to be present, as is the case with angular motion.Douglas
Sun. 22, Jul 2012, 01:56

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