How Do Towels Stay on Hooks?

In the original photo,It looks to be quite unbalanced front-rear, and a bit unbalanced left-right.OP is asking, why then does it not slip off.The answer is simply friction. That is all there is to it.Note that in the exact photo shown in the original OP:Utterly straightforward and unavoidable fact.Here's yet another hook design:It is very unbalanced front-rear, and also quite a bit to the side. Why does it not slip off? Friction. Again in this example, if both surfaces were totally frictionless: it would slip off.The answers which detail in an engineering manner where the forces lie, for some particular hook design, are fundamentally wrong.What stops a car sliding? The answer is: friction. If you make a detailed analysis of the surface area given different pressures, different concrete blends, etc, that would be fantastically helpful when eg. designing tires.But it has no connection to the answer.The "thing" that stops the car from sliding is "friction".

Consider any design whatsoever for the hook:In all cases, imagine the towel being unbalanced front-to-rear, or left-to-right (or in any direction).When unbalanced, what stops it from slipping?It's just friction.In all cases, very simply imagine just replacing all surfaces of the hook and of the towel, with more and more slippery surfaces. With perfectly slippery surfaces, it will slip off when unbalanced (absolutely regardless of design, center of gravity issues, etc).There are some really incredible howlers on this page, in the answers and comments:"Anyway I agree it's pretty obvious that friction is necessary in one direction"What does that even mean? We're talking about static (not dynamic) friction here. Of course, obviously, it's only "necessary" in whatever direction the imbalance is at the moment of discussion. (You could, obviously, of course, imbalance it the other way and then the friction would be "necessary" the "other way".) It's just a (no offense) very meaningless thought; it doesn't even parse in the normal way you talk about forces. one direction - what?"The towel is necessarily kept up by the upward force by the hook. The upward force balances the weight of the towel."Say you are discussing whether a person standing on a slope will slip sideways or not. Which is exactly the same as the question under discussion. Say you observed "Oh, the person will not fall to the center of the Earth - because the ground pushes upwards with equal force!" It is an incredibly misguided and confusing observation. What is under discussion is whether static friction will be overcome and the shoes will slip.The answer which is currently ticked contains just staggeringly, amazingly, incorrect basic physics -Therefore, the weight of the fabric forced into the "throat" of the hook (and the wings which hang from it), needs only offset the weight of the fabric that remains on the front side of the hook, which is only a very small amount of the overall weight of the towel (and therefore only needs a very small amount of fabric in the throat of the hook to offset it).

Looking from the top of the hook, you can draw (if you wish, for some reason) any normal around the 360 degrees, and note the weight imbalance on either side of that normal. But of course you wouldn't do that, you'd just have some vector, which would point in a particular direction being the current overall weight imbalance. It's (A) utterly meaningless to talk about "offsets" on some particular normal and (B) who cares? All you do is state, the imbalance is such and such, in such and such direction.But doing any of that is remarkably unclear. Quite simply, in the OPs photo - you could move the towel around, left, right, sideways - whatever - and in many cases it would still hang there even though it is unbalanced. Why? Obviously friction.The very question itself has a huge, huge howler (which - incredibly, given the length of the false analysis, nobody even noticed)There is sufficient friction between the towel and the hook to counteract the force of the towel pulling down.Heh, the force cause by the imbalance is lateral - horizontal. Nothing at all to do with "downwards". (Looking from the top - overhead - it will slide sideways (in any direction, from 0 to 360 degrees, as seen from the top) if you set it as too imbalanced in that direction.Perhaps most amazingly -There is some contribution from the friction of the various surfaces, but the main factor is the balancing of weight.

What does that even mean?(i) "the main factor is the balancing of weight" well yes, this question is about the towel being unbalanced (at some angle, 0-360, looking from the top). There's no "factor" about "balancing of weight". You would simply write down, the towel is unbalanced (say, 400 grams) in some direction (say "213 East of North".)So there is a static force supplied by X grams in direction D. OK.(ii) "There is some contribution from the friction..." what else can "contribute" to one surface against another not slipping, other than static friction? Can anyone state anything else?There are numerous other "howlers" on this page, and I do not have time to point them all out unfortunately!.Towels (and coats) are often stored on hooks, like this:

To the untrained eye, it looks like the towel will slide off from its own weight. The hook usually angles upwards slightly, but a towel does not have any "handle" to string around and hang on to the hook -- this makes it seem like it will simply slide off.Yet these hooks hold towels well, even heavy bath towels. Why?I have three ideas:

There is sufficient friction between the towel and the hook to counteract the force of the towel pulling down.The hook is angled such that the force is directed into the hook, not directed to slide the towel off of it.The center of mass of the towel ends up below the hook, since the towel is hanging against the wall.

Which of these ideas are likely correct? I am also happy with an answer based purely on theoretical analysis of the forces involved.