[AllenG (OP)]

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

[yor_on]

Wouldn't that be inertia working? As you move your glass clockwise your hand will describe a small circular movement, but your glass want to stay the same, the liquid as it starts to swirl around in the glass has a very little viscosity index vis a vis the glass so it don't really succeed in 'taking' the glass with it. The result would then be that the glass stays still, but due to your rotating movement the effect on the glass will seem to be f ex. counter clock wise and your liquid will be rotating clock wise. Or, are you saying that they really go two opposite ways? Send us a *.gif, with the wine rotating too

It seems to me like you will have three movements if so. One is your hands movement, the other will be the glass going counter wise to your hand and the third will be the liquid following your hands movement? It must involve the principle that for every action (wine swirling) there is a reaction if so (glass moving opposite way) but I tried your experiment (well, hastily:) without getting this effect?

[lightarrow]

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

Allen, I used to ask this as physics question to my collegues at university... []

The effect is very interesting, infact.

This is my answer: when you rotate the glass, for example clockwise, the part of the glass' base which is more far from the rotation's centre moves faster, so the friction with the table is stronger, so on the glass' base there is a net momentum of forces directed anti-clockwise.
It's difficult to explain without a draw, I hope you have understood. In case, ask again.
lightarrow.

[lightarrow]

Wouldn't that be inertia working? As you move your glass clockwise your hand will describe a small circular movement, but your glass want to stay the same, the liquid as it starts to swirl around in the glass has a very little viscosity index vis a vis the glass so it don't really succeed in 'taking' the glass with it. The result would then be that the glass stays still, but due to your rotating movement the effect on the glass will seem to be f ex. counter clock wise and your liquid will be rotating clock wise. Or, are you saying that they really go two opposite ways? Send us a *.gif, with the wine rotating too

It seems to me like you will have three movements if so. One is your hands movement, the other will be the glass going counter wise to your hand and the third will be the liquid following your hands movement? It must involve the principle that for every action (wine swirling) there is a reaction if so (glass moving opposite way) but I tried your experiment (well, hastily:) without getting this effect?

Actually, the effect is present even without any liquid inside (as Allen explaines).

[yor_on]

Was it on the table?
I need to get my sleep right, and glasses too.
Awh

[AllenG (OP)]

Allen, I used to ask this as physics question to my collegues at university... []

The effect is very interesting, infact.

This is my answer: when you rotate the glass, for example clockwise, the part of the glass' base which is more far from the rotation's centre moves faster, so the friction with the table is stronger, so on the glass' base there is a net momentum of forces directed anti-clockwise.
It's difficult to explain without a draw, I hope you have understood. In case, ask again.
lightarrow.

I think I'm following you.
Is this an example of precession, and why my French bicycle's left pedal will loosen over time?

"Precession" refers to the tendency of a part subject to rotating stresses to rotate in the opposite direction of the stress rotation. In bicycle applications this becomes a particular issue with the threads that hold pedals into the crank, and the threads that hold the bottom bracket assembly into the frame.

[/url]

[lightarrow]

Allen, I used to ask this as physics question to my collegues at university... []

The effect is very interesting, infact.

This is my answer: when you rotate the glass, for example clockwise, the part of the glass' base which is more far from the rotation's centre moves faster, so the friction with the table is stronger, so on the glass' base there is a net momentum of forces directed anti-clockwise.
It's difficult to explain without a draw, I hope you have understood. In case, ask again.
lightarrow.

I think I'm following you.
Is this an example of precession, and why my French bicycle's left pedal will loosen over time?

"Precession" refers to the tendency of a part subject to rotating stresses to rotate in the opposite direction of the stress rotation. In bicycle applications this becomes a particular issue with the threads that hold pedals into the crank, and the threads that hold the bottom bracket assembly into the frame.

[/url]

No, it's not precession. I don't think it has a specific name.

[AllenG (OP)]

Would this be an example of a planetary or elliptical gear system?
My fingers being the outer gear the stem being the inner.
http://en.wikipedia.org/wiki/Epicyclic_gearing

[AllenG (OP)]

An answer I got from a friend was that the glass rotates in the opposite direction because I had filled it with an Australian Shiraz.

[lightarrow]

Would this be an example of a planetary or elliptical gear system?
My fingers being the outer gear the stem being the inner.
http://en.wikipedia.org/wiki/Epicyclic_gearing

Yes, sort of.

[lyner]

Would this be an example of a planetary or elliptical gear system?
My fingers being the outer gear the stem being the inner.
http://en.wikipedia.org/wiki/Epicyclic_gearing

I like your explanation best. It will certainly account for how the glass will rotate (spin) about its axis the opposite way to the direction the stem 'orbits' around the hole made by your fingers. A clockwise 'orbit' will produce a reaction (friction) between your skin and the stem of the glass which is in a direction to make the glass actually spin anticlockwise. If the table top is slippery, the hand / stem friction force is the only significant one. The planet wheels in an epicyclic gear, in a similar way to the glass stem, spin in the opposite sense to the centre shaft if the outer gear (your non rotating hand) is stationary.
Precession is not the appropriate concept here, I think.
'ideal' systems are always easier to explain and describe than less well defined systems like twirling glasses.

[lightarrow]

Would this be an example of a planetary or elliptical gear system?
My fingers being the outer gear the stem being the inner.
http://en.wikipedia.org/wiki/Epicyclic_gearing

I like your explanation best. It will certainly account for how the glass will rotate (spin) about its axis the opposite way to the direction the stem 'orbits' around the hole made by your fingers. A clockwise 'orbit' will produce a reaction (friction) between your skin and the stem of the glass which is in a direction to make the glass actually spin anticlockwise. If the table top is slippery, the hand / stem friction force is the only significant one.

I don't think you would have any effect at all if the table top were totally slippery.

[AllenG (OP)]

I repeated the experiment.


And did it with the glass upside down.


In both cases I'm swirling the glass counter clockwise (anticlockwise).

[lightarrow]

I repeated the experiment.

In both cases I'm swirling the glass counter clockwise (anticlockwise).

The effect on the second case put me on the spot.
Don't know, maybe in that case, with that glass' surface (at those speeds) friction decreases with speed, instead of increase (as in the first case).

[yor_on]

If.... this is a 'real' effect the only difference between Gif:s seems to be the amount of material in contact with the table. That seems to hint to some sort of frictional effect, but how that then would produce a counter clockwise motion beats me? Friction slow things down, but I've never heard it change a direction to the opposite?

[AllenG (OP)]

With the glass upside down it would tend to roll along the glass' rim, and the lower center of gravity is quite noticeable.
I think the difference between the two is the amount of friction between the glass and the table.
I still think with the glass right side up it is an elliptical gear system, with the friction between my fingers and the stem being greater than that between the glass and the table.
Upside down, the amount of surface contacting the table is greater than the friction between my fingers and the stem.

[lightarrow]

With the glass upside down it would tend to roll along the glass' rim, and the lower center of gravity is quite noticeable.
I think the difference between the two is the amount of friction between the glass and the table.
I still think with the glass right side up it is an elliptical gear system,
with the friction between my fingers and the stem being greater than that between the glass and the table.
Upside down, the amount of surface contacting the table is greater than the friction between my fingers and the stem.

[]
I don't think it depends on the friction between your fingers and the stem. Can you try with something else, instead of your fingers, like a rod with a ring on one end, wich could make very little friction with the stem, or something of that kind?

[AllenG (OP)]

With the glass upside down it would tend to roll along the glass' rim, and the lower center of gravity is quite noticeable.
I think the difference between the two is the amount of friction between the glass and the table.
I still think with the glass right side up it is an elliptical gear system,
with the friction between my fingers and the stem being greater than that between the glass and the table.
Upside down, the amount of surface contacting the table is greater than the friction between my fingers and the stem.

[]
I don't think it depends on the friction between your fingers and the stem. Can you try with something else, instead of your fingers, like a rod with a ring on one end, wich could make very little friction with the stem, or something of that kind?

Can't use a ring (won't be able to get it around the base) but I did try it with an open ended wrench, the effect was the same as with my fingers (although the glass moved more slowly).
I'll post a .gif but it has to wait until after Easter Sunday lunch. 

[AllenG (OP)]

I was wrong about the upside down glass having a lower center of gravity.  The base of the glass weighs more than the bowl part.
Right side up the glass' CoG is closer to the table, upside down it is farther away.
When I have the glass upside down the tendency is for the glass to become off balanced and roll along its edge.

In the distance the sound you hear is my family telling me to quit playing with the stemware and sit down to eat.
I'll return to this later.

[lyner]

Would this be an example of a planetary or elliptical gear system?
My fingers being the outer gear the stem being the inner.
http://en.wikipedia.org/wiki/Epicyclic_gearing

I like your explanation best. It will certainly account for how the glass will rotate (spin) about its axis the opposite way to the direction the stem 'orbits' around the hole made by your fingers. A clockwise 'orbit' will produce a reaction (friction) between your skin and the stem of the glass which is in a direction to make the glass actually spin anticlockwise. If the table top is slippery, the hand / stem friction force is the only significant one.

I don't think you would have any effect at all if the table top were totally slippery.

I think we may all be talking at cross purposes.
If it is as I imagine, I think the only effect of the table (essentially) is to keep the glass upright - or it would precess / flip. The epicycle effect is the best way to explain the phenomenon as I see it; the stem of the glass drags against the inside of the 'hole' and, because the internal circumference of the hole is greater than the external circumference of the stem, each orbit requires the stem to spin to make up the difference in circumferences. The bigger the stem, the less rotation I would expect.

There is a slight ambiguity, AllenG, about your movies. Is the glass held loosely, so it can move about inside the 'hole' (which is the situation I am considering) or firmly (as in a bush-type bearing)?  Also - it is not clear whether the hand is moving in a clockwise or anticlockwise  sense. If you could draw an arrow on the table to show this, it may help me.

It may be that AllenG's question would also relate to the motion of a spinning top / glass /plate as it  slows down and eventually comes to rest - in which case I would agree with lightarrow about the need for friction against the table top.