Re: Weight of a Juggler

["Folkerts, Timothy J" <FolkertsT@BARTONCCC.EDU>]

Jack wrote:
> At the 1 sigma level I see no change.  The experiment needs considerable
> refining.  Can you break the fluctuations into a time varying part with
> an accurately measured amplitude and "noisy" part due to measurement
> uncertainty?

The first sentence was exactly my point - the results of a simple, fun, 1 hour experiment confirm that the "average weight" is independent of any juggling.


As for refinements, let me give a few more details.  Each trial collected data for 10 sec @ 20 points/sec.  Only the last 6 seconds were used in the analysis (I was doing this by myself and needed a moment to start the experiment and get into a steady rhythm).  The data clearly showed a frequency equal to the frequency of the throws.  The 0Hz (standing still) showed no particular pattern, so the 0.9N st.dev. is presumable the minimum noise to be expected (some combination of instrument variation & breathing/other slight motion).

The amplitude of the variations above and below the average were relatively constant for each run but increased as the frequency decreased (a few, big throws = a few, big variations).  For example, for the middle rate the lowest scale reading for each cycle varied from about 780N to 820N, while the peaks ranged from about 910N to 940N, with the average of 873N (Interestingly to me, the sharpest feature is the valley, not the peak).

If I were to do this more seriously, some of the refinements could be
* longer data collection
* varying weights
* varying juggling patterns
* videotaping
* a metronome to maintain a steady pace
* repeating the trials
* analyzing the height of the peaks & valleys (mean, st.dev, area, etc)
* finding a second juggler to reproduce the results
* calibrate the scale; check linearity; check response time
* an assistant to start the experiment
* $100,000 NSF grant ;-)

Are those the sorts of refinements you were thinking of?

Tim F


P.S.  I just by accident saw an old Vernier newsletter where someone used gloves with wires to detect and time the catches of metal objects while juggling.  I suppose I could do something like that as well.



Instructor of Physics
Barton County Community College
Great Bend, KS
620-792-9320
"The only thing necessary for the triumph of evil is for good men to do nothing." Edmund Burke



-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@list1.ucc.nau.edu]On
Behalf Of Jack Uretsky
Sent: Thursday, September 02, 2004 6:18 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: Weight of a Juggler


At the 1 sigma level I see no change.  The experiment needs considerable
refining.  Can you break the fluctuations into a time varying part with an
accurately measured amplitude and "noisy" part due to measurement
uncertainty?
                                Regards,
                                        Jack

On Thu, 2 Sep 2004, Folkerts, Timothy J wrote:

> I was feeling groggy and needy to get out of my seat for a few minutes, so I decided to do an experiment to confirm an old thought problem.  I got the Vernier force plate (looks and works kind of like an electronic bathroom scale) and three 0.5 kg masses and started juggling.  I juggled at different rates, but I didn't try different masses yet (partly because 0.5 kg was the heaviest set of matched objects I could find in a shape that I could reasonable handle).
>
> The initial data is summarized here.
>
>   rate    mean    st.dev.
>   0 Hz    878 N      0.9
>   1.5 Hz  880 N     57.7
>   2.4 Hz  873 N     40.4
>   4.4 Hz  880 N     25.8
>
> 0 Hz is standing still holding the 3 x 0.5 kg masses.    So the answer is indeed "no", the average weight doesn't decrease when you are juggling three objects instead of holding them!  Also no surprise is that the slow juggling (which means a few big throws) had the biggest variation in force.
>
> If there is interest, I could give a few more details - or email the original files (contact me at folkertst@bartonccc.edu).  I'm thinking of expanding this into an article for TPT, so if you can think of other ideas to incorporate, I'd be interested in any suggestions.
>
> Tim F

--
"Trust me.  I have a lot of experience at this."
                General Custer's unremembered message to his men,
                just before leading them into the Little Big Horn Valley