What causes a glass of water to move on its own on a glass surface?

In summary, the conversation revolved around the topic of glasses sliding on glass surfaces. Some possible explanations were offered, including surface tension, trapped air bubbles, and condensation on the glass. The conversation also explored the idea of a tilted table or the bending of a table causing the movement. Overall, there was no definitive answer but various theories were discussed and experiments were suggested to further investigate the cause of the movement.
  • #1
ViolentCorpse
190
1
Hello!

I'm sorry if I'm posting this in the wrong section. I didn't know where else to put this.

So here's the problem: Sometimes when I put a glass of water after drinking from it on my table (which also has a glass surface), the glass slides a little bit on its own. Sometimes it happens right after I have put it on there, and sometimes it stands still where I left it and slides after some time has elapsed, comes to a stop and slides a relatively smaller distance again later! I've also observed that this only happens when the glass is wet and while, this doesn't happen every time, it has happened enough times to convince me that I'm not hallucinating.

So, it's just been bothering me what the real cause of the movement is. I'm sure as hell it's not magic.
 
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  • #2
I've noticed this too - but only for some glasses. I was wondering if it was something to do with the shape of the base of the glass? For example it has never happened to me with a wine glass, or a mug, but a tumbler does do it. I had previously thought there had been trapped air underneath the glass which had managed to escape, moving the glass, but I don't think this is right. Could it be a surface tension thing?

OK, going to go and experiment...
 
  • #3
I've had this happen many times at a local diner. The glasses have a flat bottom and water from condensation builds up on the glass. Eventually enough has fallen down into a small puddle that when you set your glass down you are putting in on a layer of water that allows it to slide with virtually no friction. Combine that with a very slightly tilted table and you have a glass that moves on it's own.
 
  • #4
Is that all it is? I've not been able to replicate it at home today, but I have a feeling the glass moves in a non-consistent direction. Could the movement come from the fluid under the glass readjusting to a uniform thickness?

Time to go the the pub and try more experiments there.
 
  • #5
Rooted said:
Is that all it is? I've not been able to replicate it at home today, but I have a feeling the glass moves in a non-consistent direction. Could the movement come from the fluid under the glass readjusting to a uniform thickness?

Time to go the the pub and try more experiments there.

I'm not sure. My glass always slides towards the edge of the table at the diner.
 
  • #6
Yeah! My glass always slides toward the edge of the table too. I never thought that the table could be tilted, because... it doesn't appear to be, heh. :p

Thanks Drakkith.

@Rooted: Let me know if you find something cool with your experiments.
 
  • #7
ViolentCorpse said:
Yeah! My glass always slides toward the edge of the table too. I never thought that the table could be tilted, because... it doesn't appear to be, heh. :p

Thanks Drakkith.

@Rooted: Let me know if you find something cool with your experiments.

The table doesn't really even need to be tilted. It could be bending very slightly under elbows and such as well. And it doesn't take very much tilt or bending to produce movement when you are floating on a liquid.
 
  • #8
Yes, very reasonable.

Thanks Drakkith! :)
 
  • #9
My guess is that you have an air bubble trapped under the bottom of the glass, maybe it expands slightly causing the glass to move?
 
  • #10
QuantumHop said:
My guess is that you have an air bubble trapped under the bottom of the glass, maybe it expands slightly causing the glass to move?

Why would the air suddenly expand? Do you think this is a better explanation than the one I gave already?
 
  • #11
Drakkith said:
Why would the air suddenly expand?

He doesn't mention if its a cold drink or a hot coffee in a glass mug, I've seen plenty of bubble come out from underneath a cup on a wet surface.

Drakkith said:
Do you think this is a better explanation than the one I gave already?

I think both answers are plausible but why do you ask?
 
  • #12
QuantumHop said:
He doesn't mention if its a cold drink or a hot coffee in a glass mug, I've seen plenty of bubble come out from underneath a cup on a wet surface.

I think he was talking about cold drinks since he was saying talking about condensation on the glass.

I think both answers are plausible but why do you ask?

I have a hard time believing that gas expansion from a hot drink that is on liquid would cause much. The difference in temperature simply isn't that much. However, I can't say for sure.
 
  • #13
Drakkith said:
I think he was talking about cold drinks since he was saying talking about condensation on the glass.

He doesn't use the word "condensation" anywhere in this post!

Drakkith said:
I have a hard time believing that gas expansion from a hot drink that is on liquid would cause much. The difference in temperature simply isn't that much. However, I can't say for sure.

He was asking a question and I just threw in possible answer, I don't see the problem with that.
 
  • #14
QuantumHop said:
He doesn't use the word "condensation" anywhere in this post!

True, but he did say "when the glass is wet", which I took to mean condensation.



He was asking a question and I just threw in possible answer, I don't see the problem with that.

There is no problem. This is a forum and things are open to discussion. I just don't think that a hot beverage is going to cause gas to expand and slide anywhere. But, as I said, I am not sure, as I am only one person and have been wrong plenty of times in the past. If you think differently you could try and convince me otherwise.
 

1. How does the movement of the glass affect the water inside?

The movement of the glass can cause the water inside to slosh around and create waves. This is due to inertia, as the water wants to stay in its original position while the glass is moving.

2. Why does the water in a glass sometimes seem to move on its own?

This is most likely due to evaporation, where the water molecules at the surface of the glass gain enough energy to break free and enter the air as water vapor. This causes the water level to slowly decrease over time.

3. Can the movement of the glass affect the temperature of the water inside?

Yes, the movement of the glass can affect the temperature of the water. When the glass is moved, the water molecules are also moving and colliding with each other, causing friction and increasing the overall temperature of the water.

4. How does the shape and size of the glass affect the movement of the water inside?

The shape and size of the glass can affect the movement of the water inside in various ways. A taller and narrower glass may cause the water to slosh more due to its higher center of gravity, while a wider and shorter glass may have less noticeable movement.

5. Does the type of liquid in the glass affect its movement?

Yes, the type of liquid in the glass can affect its movement. Different liquids have different viscosities, or resistance to flow, which can impact how they move in response to the movement of the glass. For example, a glass of honey will have much slower and more sluggish movement compared to a glass of water.

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