I've been pondering about something i experienced the other day, hope you smart people might help :) I was holding a glass of wine, filled half way more or less. And at some point i was swirling the wine, by holding the glass at its neck and making circular clock-wise motions parallel to the table. Sort of like drawing circles with it on the surface of the table. While I was doing that, I noticed that the glass itself was spinning counter clock-wise on its axis, which is perpendicular to the table. So my question is,how does this happen? Is it the product of conservation of the angular momentum? By that the glass is responding to the wine spinning inside of it, and spins back trying to keep the total angular momentum at 0? does the friction between the wine and the inner part of the glass makes a difference in the outcome? I wonder... By the way, after a few sips, I tried spinning the glass once again. Same results, but not as strong of a reaction regarding the more full glass. What do you think?
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$\begingroup$ I think you're feeling Gyroscopic precession. But it's hard to understand the question. $\endgroup$– Brad SCommented Apr 7, 2017 at 15:31
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$\begingroup$ "I felt the glass spinning on its own axis...on the direction opposite to the one the entire glass was spinning". I think you have a typo, please correct and clarify if you want an answer. $\endgroup$– anon01Commented Apr 7, 2017 at 16:10
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$\begingroup$ Alright, i made some changes $\endgroup$– Adi CohenCommented Apr 7, 2017 at 17:05
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1 Answer
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As you move the full glass, this tosses the contents around the inside (swirling).
Even if you're not attempting to tip the glass, the force of the liquid on the vessel is going to (slightly) tip it. You can imagine that as the liquid is farthest from you, the glass is also slightly tipped away from you. This means the strongest contact with the table is also at the point on the base farthest away from you.
At this point in the motion, you are pushing the glass to the right. But since it is leaning, the frictional forces are not equal over the base. They are strongest at the far edge. This creates a torque that serves to spin the glass to the left (or counterclockwise).
answered Apr 7, 2017 at 18:08
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$\begingroup$ Your explanation sounds very plausible! $\endgroup$ Commented Apr 7, 2017 at 19:00