Or rather, what exactly does water do to help certain surfaces become more “squeaky”?
Example 1: If you’re like me, you have fond images from childhood of seeing some self-made musician on tv who could coax a tune from brandy snifters and other assorted glassware by rubbing his finger(s) across their lips. The guy would have to keep wetting his fingers to keep the music a-comin’.
Example 2: I have this pair of boots, with rubber soles, that squeak like mad when I walk on a very smooth floor - but only when they’re wet on the bottom. If they’re clean but dry, they squeak not.
How come? What does the addition of water do in the above two cases? Does it allow a squeak-type sound to be produced by decreasing the friction between the two surfaces? (If so, why wouldn’t oil have the same effect?) Or, does it increase the friction? Or, is it more complicated than that?
Just a WAG here, but I’m guessing that as you move your finger (for instance) across the wet surface, your skin sticks a little due to the moisture and stretches a bit before pulling free and relaxing and starting the process over again. When it pulls free, it makes a little noise, and the sum of all of these noises so close together is the sound we know as a squeak. When the surface is dry, the friction is lower, so your finger just slides smoothly and quietly along.
“There are only two things that are infinite: The Universe, and human stupidity-- and I’m not sure about the Universe”
–A. Einstein
Well I don’t know, but my guess is that the friction is static when the boot is dry (not slipping), dynamic when it is oily, and a combination when it is wet.
I think that the sound comes from the boot starting and stopping very quickly and pulling at the floor when it does so. You never hear squeaking when the boot is slipping steadily I bet.
Anyway I don’t know, but it seems like a sensible explanation.
I believe the previous posters have it in the right direction, but I’d like to elaborate a bit more. Friction is a result of the breaking of chemical bonds between two surfaces. The squeaky sound that you hear is produced when these bonds are broken as one surface slides across the other.
The underside of your boot and the ground you walk on is generally not a very clean area, and it they are likely coated with a layer of dust on the microscopic level. When you slide across the floor under these conditions, the dust particles act as a lubricant in the process. They don’t bind very well with the ground or boots, they are irregular in shape and decrease the actual area of contact between the two surfaces, plus they would probably roll instead of slide as the two surfaces move pass each other.
I don’t have an absolutely correct answer to the OP, but I do have a few ideas. The first that comes to mind is that water washes your boots clean, making sure that at least one surface is devoid of dust particles. If you then walk on a relatively clean floor, your boots can form chemical bonds more readily with the floor without obstruction from dust. As these bonds break when you slide forward, you get the hallmarked squeaky sound. In addition to this, whatever dust still present will be suspended in the water. This means that when the weight of your body presses downwards, the dust will be pushed out of the way into the grooves on the bottom side of your boots. And finally, water is a polar molecule, whereas oils are not. Perhaps the strong polarity of water molecules can turn it into a good adhesive between your boots and the floor, thus contributing to the squeaky sound.
Uh. I think this is much better explained by simple physics rather than simple chemistry. I also don’t think it has anything to do with dust. A clean boot will squeak on a freshly mopped floor.**
I think you have the wrong idea. In this case water is a lubricant, not an adhesive. Oil is a much better lubricant. Dust is not an issue really, and IMO the squeaking is caused by the breaking of physical bonds (i.e. static to dynamic friction) rather than chemical bonds (yeah I know it’s all really chemical bonds, but all chemical bonds are really physical bonds, it’s a moot point).
According to Chronos’s WAG up above, which sounded convincing enough when I first read it, your skin (or boot, as the case may be) sticks because of the moisture. In other words, the water is increasing the friction here, right? Zor’s post, suggesting that the water is acting as an adhesive here, would seem to concur on this point.
But according to KarmaComa, the water here is acting not as an adhesive, but as a lubricant, though not as good a lubricant as oil. Isn’t a lubricant defined as something that lessens friction? Extrapolating from this view, would you say that the water decreases the friction only to the extent that it lets your skin/boot “slip” a little bit in the first place, whereupon it quickly catches again on the smooth surface? A lubricant that decreases the friction significantly more this will let you slip but not stick, thus eliminating your squeak. Sound right?
I agree that dust is not really an issue. But it’s still intersting to consider as a case by itself, since fine dust can also be seen as decreasing the friction between boot and floor, but not in such a way that it makes your boot squeak. Because it’s too good a lubricant?
I know I must be making this more difficult (for myself) than it really is. I just want to be able to squeak to my heart’s content and understand the physics as I do so! Thanks for your input.