Well, its answer is very simple. Watermelon does not sink in the water due to some simple reasons. First of all it has the air in it. So when a thing has some air in it and the that thing is also air tight i.e there is no way from where air can leak than that thing would totally behaves like a tube. I meant to say from tube is swimming tube. If you'd put the tube of some tire of a car while it is full of air it would not sink as well. And that is the same case which is applied on watermelon. Watermelon also has air in it and the air has no way to come out from it until you'd cut it. So if you'd cut it it will sink in the water. That is the reason due to which watermelon does not sink in the water and it keeps floating on the surface of water. I hope you've understood the reason because of which watermelon floats on water. Thanks for asking.
