Why does a place of wood floating on water have no Brownian motion?

Explanation

The piece of wood is very large compared to the dimensions of water molecules. At every instant, a very large number of moving water molecules collides with this piece. The force exerted in any direction due to some colliding molecules is cancelled by the equal and opposite force due to some other molecules. As a result, the resultant force on the piece of wood becomes zero and it has no Brownian motion.