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For example, if you think the frictional force is some function
of velocity, you can write
dv/dt = F(v)
and you can visualize the force law by plotting dv/dt as a
function of v.
It is well worth doing this for the old and new spinner data.
For the data BC got from the web, the plot is here:
https://www.av8n.com/physics/img48/fidget-spinner-force-law.png
The red line is a fitted parabola, mostly drag proportional to
v^2 but with a small linear component that is noticeable at
small v.
For the data that BC took yesterday, the situation is markedly
different:
https://www.av8n.com/physics/img48/bc-spinner-force-law.png
For one thing, we notice that the speeds are an order of
magnitude smaller. It appears that the v^2 term (presumably
aerodynamic drag) is not noticeable here. There is a small
linear term, plus a constant term. The constant term goes
away at the very smallest speeds, as it must, since the net
force must go to zero at zero speed.
I do not have a microscopic physical explanation for the
constant term. It will require more thought than I can give
it at the moment.