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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.
Re: just one more thing...
Date: 2008-02-06 10:41 pm (UTC)What you said about the buckled part being pulled back into place is true, but I'm not sure that there is ever any buckling.