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I am looking for an animation or even better a video with a real experiment, which shows that at constant flow rate the speed of water in a pipe is higher at narrower parts of a pipe.

Water flow from Halliday

I googled for hours but didn't find any material. So if someone knows good animations or videos for this, please let me know!

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3 Answers 3

up vote 3 down vote accepted

Try http://youtu.be/DOUfyDHxkYQ?t=4m53s (the relevant visualisation starts at around 4:53, but if you watch from the beginning it shows you how the experiment is set up and demonstrates other things such as stream lines), or http://youtu.be/LI9Mi1KhFTs?t=3m4s

They're from a series of films made in the '60s by the "National Committee for Fluid Mechanics Films", which are a rather nice resource in general for videos of fluid dynamics demonstrations. This page has them all in RealPlayer format - I usually get the title from that page and then search for it on YouTube, since it's more convenient.

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I dunno about a video, but you can certainly show this at home:

  • Blow water through a hose with a nozzle
  • Show how faucet water decreases in radius as it falls (since it becomes faster)
  • Cinch half the opening of a straw
  • Fill a funnel, while keeping the neck blocked. Now, unblock it, and see how water comes out pretty fast but the water level inside decreases slowly.
  • (Credit @MikeDunlavey) Not a water example, but notice how traffic slows down at bottlenecks and speeds up th moment you exit one.
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+ Also, the next time you're stuck in traffic because the road is narrow ahead, notice how you move slowly until you get to the narrow place, and then you move fast. –  Mike Dunlavey Mar 18 '12 at 12:58
    
@MikeDunlavey True. Though in that case, stress/pressure increases in the bottleneck :P –  Manishearth Mar 18 '12 at 13:08

In the meantime I found this short animation:

http://www.youtube.com/watch?NR=1&feature=endscreen&v=k8IRxT1sM6s

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