Science a GoGo's Home Page Forums General Discussion Not-Quite-Science Forum Don't tell me to 'google' this...

If I have two straws, with one having a radius that is 1/2 of the other, and I put the smaller one in the bigger one, and drink water through the two straws, what path would the water take and why?

I would think more fluid would travel up around the outside of the smaller straw - there will be slightly more resistance in the central straw.

Try Googling it.

Blacknad.

Why will there be slightly more resistance in the central straw?

And if that "Try Googling it" statement wasn't sarcastic then you're just a weirdo.

There's going to be some friction between the walls of the straws and the liquid, and since there is more surface area per volume in the smaller straw, there's going to be more friction on liquid passing through that one.

Have you tried googling it?

yeah. I have.

Thanks for the explanation, I see now...

"And if that "Try Googling it" statement wasn't sarcastic then you're just a weirdo."

Weirdo I may be, but sarcastic I wasn't - I was trying to joke 'with' you, not at your expense.

Blacknad.

Yeah, I thought so... You should have included an emoticon to make it more clear that you were joking.

And you may be wrong, the same amount of liquid may travel up both straws but one at a slower rate, due to friction. Just a thought...

I'll include emoticons, but I hoped you would know by now that I very rarely stoop to sarcasm.

As for the fluid - I can't see how the same amount of fluid will travel up the centre straw if it is slower. It is also not really about friction as I see it. It is simply that there is much more room around the inner straw so the flow will be much greater.

Regards,

Blacknad.

It is about friction, and any other attraction between the fluid and the walls of the tube. See: http://www.engineersedge.com/fluid_flow/flow_velocity_profiles.htm

Thanks Soilguy.

Blacknad.

Hi soilguy:

I just happened to notice this post.

I checked your link and it was informative.

When dealing with a straw within a straw takeing fluid from the same source with equal suction levels being applied does not the expeirment double the friction? The area within the larger straw has more then twice the surface contact than that contained in the smaller straw. Your link did not decide that hypothetical setup.
Of cvourse, we do not have precise internal and external demensions for the straws or for their length, surface composition or the viscosity of the fluid involved. I doubt Google will help.
Just an observation, I have tried to answer it.
jjw

Correction
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/
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I have NOT tried to answer it.
jjw

Jim,

You can edit your own posts at any time by clicking on the paper and pencil icon at the top of the posting.

Amaranth

Actually, an interesting question.

Assuming that equal pressure is applied,(unlikely but what the hell...):

Take the dia. of the small straw as 2 unit, the larger at 4 units.

This gives:
Area Cir. per. of Ratio of
channel Area/Per.
Small straw; 1 Pi 2 Pi 2 Pi. 1/2
Large straw; 4 Pi 4 Pi
Outer Ch. ; 3 Pi(L-S 6 Pi(L+S) 1/2

Neglecting boundary layer width as a factor, (its effect being
dependant on flow velocity and we don't know it anyway), the
resistance should be the same.
I would guess however that the boundary layer width in the
narrower outer chanel would govern.