If to throw a small stone or a copper coin into water, they will immediately go to a bottom. Why then the massive and heavy wooden log does not sink, and only slightly plunges into water? Here laws of physics work. The ability of objects to float is explained the surface of liquid by differences in density of substances.
What is density
In physics mean the physical quantity in which the weight and volume of any body among themselves correspond by substance density. Density – essential and rather constant sign of substance which is widely used for recognition of various materials which nature is not measured by eye.
Knowing substance density, it is possible to establish body weight.
Any bodies which surround the person in everyday life consist of various materials or substances. People in life and production activity often should deal with metals, wood, plastic, a stone and so on. Each material has the density. For this reason the mass of two different objects having the identical volume, a form and the sizes, but made of different substances will be various.
Why the log does not sink
Differences in density of water and wood just also allow a heavy and massive log not to sink, and to float surely. The fact is that under normal conditions density of water is equal to unit. And here at a tree this indicator is much lower. Therefore the weighty piece of a dry tree keeps on the surface of liquid, is absolutely insignificant plunging into it. However also the tree under certain conditions is capable to drown. If the log a long time was in water, it gradually becomes impregnated with moisture and bulks up. In this case density of a log changes and can exceed liquid density. This phenomenon was often observed during industrial alloy of logs on water when they were overtaken to the place of processing in the natural way, without use of transport. On the rivers, in places of the strengthened timber-rafting, it is still possible to find so-called toplyak. It logs which in whole or in part sank laid down on a bottom or hung in slightly waterlogged state. Toplyaki cause many troubles to amateur fishers. They also constitute danger to the vessels moving with a high speed.
The waterlogged log which one end acts from water is capable to damage a ship covering.
In the nature also breeds of the trees called "iron" which density exceeds water density grow. It is possible to give a black rosewood and a parrotiya as an example Persian. Wood of these plants very dense also differs in hardness. Fabrics of such trees are plentifully impregnated with oils that interferes with their rotting. These breeds are very much highly appreciated, widely apply them in production of furniture. Here only to sweep on a log from a "iron" tree it will not turn out, it will inevitably leave under water.