(no subject)
Jan. 24th, 2008 05:39 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
jackhttp://www.straightdope.com/classics/a4_184.html
Straight dope asks "How can you suck a strand of spaghetti?" The question being, sucking a liquid, you create a vacuum in your mouth, and it's generally enough to say the pressure within the liquid is less than that in the mouth, so a force acts on the liquid in the straw. Sucking a solid object (eg. pencil), you can say the air pressure cancels out all over, except down the length.
But spaghetti is floppy. The air pressure on the *end* of the strand can't be relevant, because pushing their wouldn't force it into the mouth.
The answer doesn't seem very satisfactory. I'm sure it's something like, air pressure generally acts all over the surface, perpendicular to it, and this cancels out all over[1]. Except on a line through the part of the strand through the lips. So there's a force on that part, propagated down the strand to the next bend (where it acts sideways to the strand).
But I can't really put that into words (or symbols). Can anyone else provide a simple, satisfying description?
[1] May be hard to show, either by common sense or integrals, but we know it *does* because the net air pressure on a strand of spaghetti in midair (neglecting variations with height) is zero everywhere.
Straight dope asks "How can you suck a strand of spaghetti?" The question being, sucking a liquid, you create a vacuum in your mouth, and it's generally enough to say the pressure within the liquid is less than that in the mouth, so a force acts on the liquid in the straw. Sucking a solid object (eg. pencil), you can say the air pressure cancels out all over, except down the length.
But spaghetti is floppy. The air pressure on the *end* of the strand can't be relevant, because pushing their wouldn't force it into the mouth.
The answer doesn't seem very satisfactory. I'm sure it's something like, air pressure generally acts all over the surface, perpendicular to it, and this cancels out all over[1]. Except on a line through the part of the strand through the lips. So there's a force on that part, propagated down the strand to the next bend (where it acts sideways to the strand).
But I can't really put that into words (or symbols). Can anyone else provide a simple, satisfying description?
[1] May be hard to show, either by common sense or integrals, but we know it *does* because the net air pressure on a strand of spaghetti in midair (neglecting variations with height) is zero everywhere.
no subject
Date: 2008-01-31 02:38 pm (UTC)Sorry, I'm slightly confused here, did you read the other comments? Quite likely you're entirely right, of course, "the reason you can suck spaghetti is the same as why you can suck anything else" seems a much more natural theory, and "cooking reduces the friction" and "you imagined that spaghetti had to be squeezed more" would be good explanations of what I observed.
(And what was that about someone saying something was "obvious"? I'm sorry if I or anyone sounded facile, I didn't think anyone *had* been blithely assuming anything about friction, just guessing, without certainty that they were righht...)
But your comment sounded confusing to me, it sounded like hairears had a plausible theory, and you came along and said "no, that's all wrong, its the obvious way," but without actually saying how you could tell the difference. But I don't think that's what you did mean, but I'm not sure what you did mean.
If you assume a normal sucking procedure applies to spaghetti, and the wedge theory is wrong, what experiment would show for sure -- we ought to be able to show it easily, oughtn't we?
no subject
Date: 2008-01-31 11:12 pm (UTC)That's what I'm asserting. But I'm not a strand of spaghetti...
I did read the other comments, but they seemed based on the assumption that spaghetti being the same as everything else was wrong.
hairears asserted that:
"the atmospheric pressure on the very end of the strand exerts a negligible force compared to the friction at your lips."
I didn't mean to imply that anything said was facile, I'm just failing to express myself clearly due to posting on-my-way to things/otherwise in a hurry.
Hairears' theory suggested that the spagetti expanded inside the mouth, causing it to press against the inside of the mouth. This would not work, because there would be no force to press the spaghetti and the mouth together (I think, but I'll think about it). It mostly just seemed over-complicated, and likely to produce a smaller force (if it does work) than the direct sucking method, especially as spaghetti doesn't expand very much.
I would suggest that if you coat dry spaghetti in oil, it may be suck-up-able.
hairears asserted that: "the atmospheric pressure on the very end..."
Date: 2008-02-01 01:28 am (UTC)no subject
Date: 2008-02-01 08:35 pm (UTC)ROFL :)
no subject
Date: 2008-02-01 08:40 pm (UTC)Hm, yes. I have pesto.
*thinks* If difference in cooking is friction, coating in substance ought to mostly alleviate that? Though its hard to tell because it might be rubbed off in mouth. But if substances are the same in all coatings, suggests just a simple matter of friction after all. If not, suggests something more weird is going on. Maybe.
no subject
Date: 2008-02-06 11:14 pm (UTC)Reason 2 is that the lower pressure inside causes the mouth cavity to contract. Take an inflated balloon and draw a circle on it, reduce the size of the balloon and the drawn circle will get smaller. Lips are pressing inwards.
I remain unconvinced that this is the main or deciding force.