[AllenG (OP)]

I'm holding the glass loosely, and moving my hand in a anticlockwise circular motion.

I think when the glass rotates opposite to the direction I'm moving my hand it is because it is a planetary gear effect, and when the glass is upside down the unbalanced glass rolls along its rim in the same anticlockwise direction I'm moving my hand.

Who knew so much entertainment could be found in twirling a wine glass.
I've been told that if I start to spin the china on the end of dowel rods I'll be banded from the house.  [:-'(]

[lyner]

And we didn't even get as far as discussing the wine!

[RD]

Papillary ridges, a.k.a. fingerprints, exert a greater frictional force when moved across a surface in one direction than another. This may account for the bias in the rotation of your wine glass when the stem is waggled between thumb and fingers: the papillary ridges acting like a microscopic ratchet causing a bias for rotation in one direction.

If the rotation is due to the papillary ridges it should not occur when wearing gloves, (e.g. rubber washing-up type).

[lightarrow]

Papillary ridges, a.k.a. fingerprints, exert a greater frictional force when moved across a surface in one direction than another. This may account for the bias in the rotation of your wine glass when the stem is waggled between thumb and fingers: the papillary ridges acting like a microscopic ratchet causing a bias for rotation in one direction.

If the rotation is due to the papillary ridges it should not occur when wearing gloves, (e.g. rubber washing-up type).

I'm pretty sure (not 100% however) that fingers' friction has nothing to do with the effect.

[lyner]

Papillary ridges, a.k.a. fingerprints, exert a greater frictional force when moved across a surface in one direction than another. This may account for the bias in the rotation of your wine glass when the stem is waggled between thumb and fingers: the papillary ridges acting like a microscopic ratchet causing a bias for rotation in one direction.

If the rotation is due to the papillary ridges it should not occur when wearing gloves, (e.g. rubber washing-up type).

I'm pretty sure (not 100% however) that fingers' friction has nothing to do with the effect.

You can get the effect I'm describing with a stick / iron bar / etc. if you use both hands. As the stick 'tumbles', tracing out a cone, it rotates backwards. Also, if you put a coin on a smooth table and invert a glass over it, you can make the coin go round and round the inside of the glass (using your wrist to 'crank' the glass in a circular motion) and the coin rotates, backwards, again as it runs around the inner rim of the glass. That is the most ideal example I can think of which corresponds to 'my' model. Those motions are like the planetary motion in an epicyclic gear.

If the question is referring to how the glass would move without the hand interacting (no friction) then the situation is like a spun coin when it rattles to the ground.

I'm still not sure which is the actual situation we are discussing. As I said before, I think the situation is too complex to discuss until we have ascertained what is actually happening.

[AllenG (OP)]

Done with a highly calibrated serving fork instead of my fingers.

[lightarrow]

Done with a highly calibrated serving fork instead of my fingers.

Very good! Did you also try lubricating the fork with a low-viscosity oil?

[Chemistry4me]

That's nice. []

[AllenG (OP)]

Done with a highly calibrated serving fork instead of my fingers.

Very good! Did you also try lubricating the fork with a low-viscosity oil?

Nope.  Non-lubricated fork.

Thanks for all the thoughts folks.
I'm going to stick with the planetary gear hypothesis.

[yor_on]

I was swirling some wine around in a stemmed glass ware and I noticed that if I held the stem loosely between my fingers it would rotate in the opposite direction than I was swirling the wine.
I tried it with and without liquid in the glass and the effect was the same.
Why does it do that?

I made a .gif file to show the effect.

Thanks,

--Allen

I hate to say this but you still haven't showed us the gif with that wine rotating in the opposite direction of the glass? And you haven't done it with the fork either?? Come on, a jug of wine, or two, ah, ok three then, how expensive can it be?

I have this idea that maybe the wine just doesn't rotate at all?
Huh?? Bring me a jug and let's explore

[Chemistry4me]

I notice something similar, when I have a cup of water/liquid and I hold it out in front of me then I spin my whole body around, the water/liquid spins in the opposite direction inside the cup.

[lyner]

I think I have sussed out the reason for the whole thing and have explained the reversal in direction when the glass is upside down.
It goes like this.
With the glass the right way up, the centre of mass is above your fingers. Assume that you hold it in the fingers of your right hand.When you push forward, there will be a slight clockwise curvature to the motion initially (your forearm, for instance, will pivot about your elbow).  I think this will continue because you are making a conscious effort at a curved motion. There will be a moment, tilting the glass outwards from the curve, causing more downward force on the table away from the centre of the curve (one section of the base will 'dig in'). The difference in friction forces  (F2 and F3) around the edge of the base will be such as to to produce an anticlockwise force on the base - turning the glass anticlockwise. On the return journey, it is the other side of the base that digs in and the rotation is in the same sense. The diagram was a bit hard to draw but I think it says what I mean.

With the glass upside down, it tilts in the same direction as you are pushing it because the CM is below your fingers. It is the opposite side of the rim which digs in more and so the rotation direction will be in the  opposite sense because F2 would be bigger than F3.

Some actual wine had to be consumed during the investigation. Cheersh!