Well-known comic the question: what is heavier - ton tree or a ton of iron? Without thinking, usually respond that a ton of iron is heavier, causing the friendly laughter of others.
Jokers probably even louder laugh if they say that a ton of wood is heavier than a ton of iron. This statement seems too, with no less than helpful - and yet, strictly speaking, this answer is correct!
The fact that the Archimedean principle is not only applicable to liquids, and gases. Every body in the air “lose” from his weight as much weight extruded body air volume.
Wood and iron, too, of course, lose in the air of his weight. To get the true weight, need a loss to add. Consequently, the true weight of the tree in our case is equal to 1 ton + the weight of the air in the volume of the tree; the true weight of iron is equal to 1 ton + the weight of the air in the volume of iron.
But a ton of wood is much more than a ton of iron (15), so the true weight of a ton of wood more true weight tons of iron! More precisely, we should say: the true weight of the tree which is in the air weighs a ton, more than the true weight of that of iron, which weighs in the air one ton.
As a ton of iron occupies a volume in 1/8 cubic meters, and a ton of wood about 2 cubic meters, the difference in the weight of the displaced their air should be about 2.5 kg. that's how a ton of wood actually heavier than a ton of iron!