pauldw
Contributor
I hesitate to post this, but I don't grasp how buoyancy works. I do understand how to get positively buoyant, negatively buoyant, and neutrally buoyant; I'm not talking about that. What's confusing is the physics. Help?
For example, people become more buoyant as they breath out their tank over the duration of a dive. Why? The tank itself hasn't changed shape, so it's displacing the same amount of water over the duration of the dive (if anything, it seems like it would have shrunk slightly over time with less pressure on the interior walls, and therefore displace a teeny bit less water over time). I gather that it's lighter over time, because air weights something and there's less air in it, but if buoyancy is caused by water displacement, how exactly is the amount water being displaced by the effectively unchanging physical size of the tank any different?
For example, people become more buoyant as they breath out their tank over the duration of a dive. Why? The tank itself hasn't changed shape, so it's displacing the same amount of water over the duration of the dive (if anything, it seems like it would have shrunk slightly over time with less pressure on the interior walls, and therefore displace a teeny bit less water over time). I gather that it's lighter over time, because air weights something and there's less air in it, but if buoyancy is caused by water displacement, how exactly is the amount water being displaced by the effectively unchanging physical size of the tank any different?