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I can solve a Rubik's Cube underwater in a swimming pool but my problem is that I can't stay at the bottom of the pool because of the oxygen in my lungs. How can I stay in the bottom without going up to the surface?

  • Take a weight with you – paparazzo Oct 19 '16 at 9:23
  • How heavy should a weight be? My weight is 85-90 kg. – Ole Petersen Oct 19 '16 at 9:36
  • Breathe out before diving? – Takkat Oct 19 '16 at 10:04
  • I can't do that. I need to hold my breath in 1min. – Ole Petersen Oct 19 '16 at 10:10
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    To do it without some form of weight, you almost have to exhale before submerging. That was helpful advice from my swimming instructor. His not-so-helpful advice was to "think like a stone" :) – L.B. Oct 19 '16 at 12:45
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Paparazzi's suggestion from comments, to dive with a weight (not bound to your body, for safety reasons -- the weight should drop away when you straighten to push off for the surface, at the least) that will overcome your natural buoyancy. You'll need to experiment to see how much weight is needed.

A milk jug or similar, partially filled with sand and then topped up with water to eliminate air, is a good adjustable weight (more sand makes it heavier under water, but the water portion is weightless when submerged). You can also tie a rope on the handle with a float on the other end, to make it easy to retrieve the weight from the bottom of the pool. Most "normal" people will require between 5 and 10 kg of sand, perhaps less if the weight is iron (like a weight plate from a barbell set) or lead (like scuba divers' weights).

Very Important!! Never do this without a "buddy", someone who can push the weight off you and assist you to the surface if you go over your allotted solving time -- if you lose consciousness underwater, alone, you will die.

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  • "perhaps less if the weight is iron" -> The matter doesn't make any difference. If you need 8kg of sand, you need 8kg of iron as well. – Evargalo Apr 24 '18 at 14:14
  • Correct. Hence your clever remark "and then topped up with water to eliminate air", which I took for granted in my comment. – Evargalo Apr 24 '18 at 15:55
  • @Evargalo 8 kg of iron will displace less water than a jug of sand and water weighing 8 kg on the surface -- so will weigh more underwater. – Zeiss Ikon Apr 24 '18 at 15:56
  • The material definitely matters. 8kg of styrofoam won't let your sink. You want to increase the combined density of you and the weight. The mass needed is related to its volume. You only need less than 2 kg of iron to be equivalent to 8kg of sand. – John Meacham Apr 27 '18 at 22:30
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NOTE: This all depends on how long you can hold your breath.

When a rocket launches, the force from the bottom of the rocket, in kids words, "fire", pushes the rocket up in simple means.

However, if the pressure was coming from the TOP of the rocket, the rocket will go down instead of up.

Now, take a very deep breath and jump into the pool. As soon as your nose goes underwater start breathing out. This is similar to the example I gave you earlier, it's like the pressure making the rocket fly, but instead the air is pushing you down. Now, you'll start going back up. When that happens start moving your arms in a way that it looks like you're "pushing the water. You can stay down for a while, but this all matters on how long you can hold your breath.

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My friend texted my and told my a solution that worked for him. The answer for him was to have dumbbells on his thighs while being underwater. He even showed my a video where it prove that it can be done.

It can be watched here https://www.facebook.com/671704706/videos/vb.671704706/10154639991754707/?type=3&theater

Thanks.

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