If I get stuck in a flood then I will take help of a wood. Why, because it never sinks. When it is put into water, it pushes down on the water and the water moves aside to make room for the itself. But keeping in mind that the wood is dry. Why, Lets see.
Wood is made of dead plant cells and contains many open spaces
. This is why it is so relatively light when
it is dry
and has a lower density than water.
It means that a unit volume of wood has less mass (and weight) than the same unit volume of water. If the wood is wet
(fresh) it has a higher density than water
as it does not have airy space and it makes it to sink in water.
In simple terms If the entire object(wood, steel, iron, etc.) displaces a volume of water which weighs less than the object the object will sink. Even so, the material of which the cells are made is still lighter than water and so wood floats even when wet. Sometimes wood becomes so saturated with water (even the exceedingly small spaces in the cell walls themselves are filled with water) that it sinks.
Isn't is great, but don't try a much heavy wood object in your bath tub !!!