Let's say I'm $1.8\ \rm m$, $70\ \rm kg$ with a fairly typical male body shape.

I hold on to the side of an otherwise normal but very deep swimming pool, then lower myself so that the top of my head is just below the water surface.

I then let go of the side of the pool. At roughly what rate (in meters per second) will I sink to the bottom?


closed as off-topic by AccidentalFourierTransform, Kyle Kanos, Chris, Jon Custer, user191954 Sep 15 '18 at 5:06

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    $\begingroup$ This depends on so many other things than just your height and mass. I'm not sure if there really is a good way to answer this without actually doing it in an actual pool. $\endgroup$ – Aaron Stevens Sep 14 '18 at 2:55
  • $\begingroup$ @AaronStevens: I was wondering if there had perhaps been many such experiments done and if we'd have it correct to at least an order of magnitude. $\endgroup$ – dtcm840 Sep 14 '18 at 2:56
  • $\begingroup$ So you just want an estimate? $\endgroup$ – Aaron Stevens Sep 14 '18 at 2:58
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    $\begingroup$ If my lungs are full, I float. If I release some air I can be neutrally buoyant somewhere in the water column. If I exhale completely, I sink. $\endgroup$ – Jon Custer Sep 14 '18 at 13:04
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    $\begingroup$ I'm voting to close this as too-broad because there aren't enough constraints. Could you add some more about the conditions for this estimation? $\endgroup$ – user191954 Sep 15 '18 at 5:05

This simply depends on your density, i.e. the ratio of your mass to your volume. Your density depends somewhat on your body build but also to a significant amount of how much air you have in your lungs. Most people don't sink at all if they have fully inhaled.

A good example of the factors involved is scuba diving, where you want your rate of sinking (or floating) to be exactly zero. A significant part of learning how to dive is "buoyancy-control" , e.g. https://www.divein.com/guide/buoyancy-control/ this is all about actively adjusting your density based using weights, air and breathing all adjusted for depth.


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