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Old 10th December 2017, 06:43 PM   #1591
lcsaszar is offline lcsaszar  Hungary
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Hi Carlo, a pendulum moves on arc, not linear. Your string should be very long so that the pickup can move horizontally, not elevating from the disc. Otherwise very clever measuring setup!
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Old 11th December 2017, 01:55 AM   #1592
dtut is offline dtut  United States
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Carlo,

I've been enjoying your elegant experiments and the interesting results. I'm building a mock-up pivoting arm which I hope will let me measure both stylus drag and 'skipping' forces. I've been thinking about niffy's posts, too, and I'm going to try an experiment with one of my old PLTs.

I'll try to post in the next couple of days.
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Old 11th December 2017, 07:19 AM   #1593
nocdplz is offline nocdplz
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You 're right Icsaszaar, completely, but for angles <4 degrees the difference is so small that even the physicists do not care. My will was simply to see - and show - what would have been the displacements with the theoretical values, compared to the real ones. Photos speak for themselves.


Doug, i'm looking forward to your work, and the data you will find.
Really, start thinking about measuring the skating, it would be nice to start discussing concrete data.

Niffy: thanks again for your contribution. Could you please post your rig for the static measurements? I would like to make precise measurements of carts -

Carlo

Last edited by nocdplz; 11th December 2017 at 07:21 AM.
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Old 11th December 2017, 07:35 AM   #1594
nocdplz is offline nocdplz
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Icsaszaar, sorry. I reread your post, which I misunderstood. Look better at the photos: the pendulum rises but the stylus that is placed on a small arm with a vertical pivot obviously remains on the disc. If not, what would you measure?
Confusion starts maybe from the photos of the pre-test with weights and pulley : there is needed that the whole mass raises (and there is not a disk).
The mass of pendulum 41gr = 0.4 N is given by rig + small arm + counterweight - VTF. Variations of VTF were compensated with small 1/2 g weights.

carlo again

Last edited by nocdplz; 11th December 2017 at 07:38 AM.
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Old Yesterday, 11:15 AM   #1595
nocdplz is offline nocdplz
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Sorry, I said not to be qualified: converting N to mN i've lost a little dot (little, but very important, of course): too many 0 on my pocket calculator
This new table hopefully correct.
Carlo
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