Why do I have to TRY to float?

Question

If I go swimming, I always have to try to make sure I don't slip under. If I lay on my back, my feet slowly start to drop and the rest of my body follows. It's not really annoying, and I can tread water like that for hours anyway, so I'm not lazy if that's what you're thinking.

I'm just curious. Most people I know float naturally. Whereas if I don't try, I sink. And also unlike most people I know, I can actually sit on the bottom of a 10-foot deep pool... Is this weird? What could cause it?

I get the feeling I'm breaking the laws of physics here...

Answer 1

Same thing happens to me.

It's that you don't have a lot of body fat on you, so there's not much boyant force from the lesser density fat is.

Answer 2

It also has something to do with bone density.  I sink like a rock.  I'm not the skinniest person in the world as well.  :)

The denser your bone structure, the more you sink.

Answer 3

The problem is that you are too skinny. Most peoples' bodies are about the density of water, which results in them "semi-floating". Fat is less dense, which results in fat people floating better (think of an inner tube). Muscle is more dense, thus, muscular people sink (think of rocks). The reason why you have to consciously try to float is that you are less dense than water. When you concentrate on floating, you inadvertently are holding more air in your lungs, which results in making your body less dense. Your feet begin to sink first because your legs are still more dense than the water since they do not fill with air as does your chest cavity. As your feet sink, it lessens the surface area you are covering, and slowly brings your whole body down. You are able to sit on the bottom of the pool because when you do, you release some of the air from your lungs making you far more dense than the water. In short, it's all a matter of density. Large bodies which weight less comparatively float, while smaller bodies which weight more comparatively sink.