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Re: [Phys-L] fidget spinner: more data, more analysis, timestamps, force-law plot



On 09/21/2017 09:45 AM, David Bowman wrote:

It seems to me that the shape of the spinner probably has the biggest
effect on whether the deceleration force is dominated by a linear or
quadratic term in speed (assuming comparable balance and friction in
the bearing, etc).

Also speed has a big effect. The second-order term will dominate
at high speeds, the first-order term will dominate at lower speeds,
and the zeroth-order term will dominate at the very lowest speeds.

Even more importantly, the quality of the bearings has a big
effect. All evidence suggests that some of the available products
have high-quality bearings, but others not so much.

BC spinner #1 has a loose bearing. This is observed explicitly,
and also implicitly at the high-speed end of the recorded data,
where the data is very messy, which can be explained by wobble
and shimmy. Furthermore, over most of the range the friction
is dominated by a zeroth-order term, more-or-less in accordance
with Coulomb's law of sliding friction
https://mech.subwiki.org/wiki/Coulomb%27s_law_of_friction
which is commonly taught in introductory physics classes as
if it were "the" law of friction, but is not the whole story:
++ It is occasionally relevant.
-- It is very often not relevant, especially for things that
spin, roll, fly, float, and/or flow, such as cars, bicycles,
airplanes, boats, sports equipment, fluids, et cetera.

I suspect that most people who buy fidget spinners never imagined
that they would have to worry about the quality.

Some kid could make a very interesting science-fair experiment
out of this.