Hi, Suppose one has a tank of water, with a plugged drain in the centre at the bottom. Let the water be rotating in the tank. Remove the plug. A vortex forms as water exits the drain. Conservation of angular momentum (well established for a vortex) ensures that the velocity of the water changes as the inverse of the radius. Since all water eventually runs down the drain, all the water increases in velocity, with the water from the edge having increased the most.
The question is, where does the energy come from to increase the velocity of the water? If the water is stationary to start with, then it comes from the change in height of the water as it leaves the tank, and the velocity at the edge automatically adjusts itself accordingly. However if the water is already rotating before the plug is pulled, then it has to end up going faster than can be accounted for by gravity. If the radius decreases by a factor of ten before the water reaches the drain, then the velocity has to increase 10 fold, and the energy per unit mass must increase 100 fold. So where does the energy come from, or for some reason, does it simply not happen, and if not, then what does happen? Regards, Robin van Spaandonk All SPAM goes in the trash unread.
