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Deep whirlpool

  1. Jul 26, 2003 #1
    Hi all,
    the other day I was in a thermal bath where they had some whirlpool jets at the bottom of a basin about breast-deep. I was standing right over the jets, and the turbulence in the water was so strong at the surface, that I couldn't stand straight but was forced to sway back and forth and was almost washed away from the position of the jets.
    I probed the ground with my toes and expected the position of the outlets to be easily detectable by a sharp vertical jet of water. But nothing! Next, I located the outlets by eye (there were maybe 5 or 6 of them, of ~1/4 inch diameter each), and put my toe on one. There was almost nothing to be felt, and I could easily block the jet with my toe.
    Forces seem to be large only when close to the surface, and very small deeper down. Any physical explanation of this?
  2. jcsd
  3. Jul 26, 2003 #2
    well I may not have the physics explaination, but I can give you the common sense one. basically being submerged in water not only makes you lighter due to buoyancy, but changes your center of gravity. And since your center of gravity is higher, you're more suceptable to currents and other objects in motion. Basically the energy from the jets has more effect because of your submergence.

    Anyone else? Does that make sense, sound partially right, with some adjustment, or do I need to lay off the beer?:wink:
  4. Jul 26, 2003 #3
    Only that the friction of the water rotating in the tub must have been pretty low so that the rate of rotation built up over time.
  5. Jul 27, 2003 #4
    Thanks indeed for your response!

    yes I agree it's much easier for the water to move me upwards when most of me is submerged. But my head & shoulders were still out of the water, so the remaining gravity was still (say) 4 or 5 kg's or so, and I couldn't feel anything like that when probing the jet with my toe. There was almost nothing to be felt.

    maybe my wording was bad, there wasn't any rotating water in a tub. It was a big basin (say 5m x 15m or so), and there was 5 or 6 jets at the center of that, at the bottom, closer than, say, 30 cm together, with the water going up vertically, and I was standing over that. Plus, the effect was immediately there as soon as the jets were powered up.
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