Physics Asked by user122395 on November 30, 2020
I happened to chance upon this video on super-hydrophobic coating on youtube,
https://www.youtube.com/watch?v=IPM8OR6W6WE
I was wondering what’d happen if I managed to coat an entire full-body diving suit (wearing a pair of tight boots instead of flippers) along with the headgear and diving apparatus, and then jumped right into a swimming pool (and no….there isn’t a ‘NO DIVING’ sign around, so don’t bring that up in the comments please), what’d happen?
I have a very strong feeling I’d go straight down to the bottom of the pool, as if there wasn’t any water in it, i’d hit the concrete and break my legs, sure, but from practical point of view, would it be the same as free-falling? I really don’t know why, but I keep getting a gut feeling that i’d still experience some buoyant force that would significantly slow down my descent as compared to simply jumping into the pool without water in it. Who do I trust here, my brain or my gut?
Also another curiosity question; say I were already at the bottom of the pool (with water) wearing this fabulous diving suit of mine. Assume the bottom of the pool isn’t tiled, so it’s all rough like the side of the pool. If I were to attempt running underwater (remember I’m wearing the suit) would I be able to ‘run’ underwater as fast as would on the pool side (no ‘NO RUNNING BY THE POOL’ sign either..)
You would still experience a buoyant force, which would be identical to the buoyant force experienced by someone with no diving suit at all. The buoyant force doesn't rely on the water sticking to you in any way; there will still be water pressure on you after all. However, assuming you were sinking, I would assume you would sink much faster than normal because presumably there is much less drag on you from the water. So compared with the no-hydrophobic case, you would experience the same "weight" but have a higher terminal velocity.
Correct answer by zeldredge on November 30, 2020
would I be able to 'run' underwater as fast as would on the pool side.
No. Even assuming you wore enough weights to counteract the buoyancy (see @zeldredge's answer), and even though your suit would not "drag" water, you still would have to push the water out of your way in order to move through it.
Nov, 2020
Not going to pretend to understand how water flows around obstacles (see https://en.wikipedia.org/wiki/Reynolds_number), but unless you are shaped like a fish, I would expect you to leave turbulence in your wake. I would expect that the kinetic energy that you impart to the water in creating that turbulent flow would be the main thing slowing your progress.
Answered by Solomon Slow on November 30, 2020
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