| The problem is that I don't mind talking physics I just hate typing....but, the reason the stuff collects in the middle is the same reason snow drifts form. The water's speed near the center is slower than the movement of the water towards the outside. The water must be a certain speed in order to break the hold the particles have on the bottom due to gravity, The speed in the center is not fast enough to break this bond.
While the particles that are on the outside move in a circle they also bounce away from and toward the center. When they move randomly closer to the center they may move into an area where the current is not strong enough to keep them moving. And there they stay. While those that move to the outside contact the wall and stay in a high energy area and continue to move util they "find" the dead zone.....just like snowflakes and trash. |