Question

why does human body float in water when we are dead and why it sink when we are alive?

Answer 1

our body's specific gravity is more than water...when water gets into our body they starts to reduce its specific gravity...so normally our body sinks in water when we are alive...but when too much water gets into our body it starts to float...in short because of specific gravity

Answer 2

I think the answer also lies in density. It is easier to float in salt water, which is more dense, than it is to float in pure or fresh water. While the density of two people chosen at random is not that different in the grand scope of things, some people have more dense or less dense bodies, which makes it easier to sink or easier to swim. If you take in a large lungful of air, you increase your surface area and volume, decreasing your density and allowing you to float more easily. In short, connecting being alive to sinking and dead to floating doesn't really cover all of the variables that will determine your buoyancy--the position your body is in would have a considerable effect as well.