text: hydrodynamics in two glasses. will the ball move? two identical glasses (cylinders) with small orifices in their bottoms are connected by a flexible tube attached to the orifices. the glasses are filled with equal amounts of water and placed at the same level. a small ball is put inside the tube. you start stirring water (rotating it by a tea-spoon) in one of the glasses. will the ball move? if yes, in which direction? does the answer depend on the position of the orifices with respect to the centers of the glass bottoms? yes, it will move.  the phenomenon responsible is known as the bernoulli effect,  and its most basic statement is that "in a flowing fluid, an increase in flow rate causes a decrease in pressure".  what you have constructed is essentially a kind of venturi tube, which is often used to illustrate the bernoulli effect.  here is a great page about venturis and the bernoulli effect: http://home.earthlink.net/~mmc1919/venturi.html  so anyway, when you stir the water in the glass, it moves faster.  if the orifice is underneath a region of quickly-moving water, the pressure above the orifice will be decreased.  this will cause the ball in the tube to move towards the lower-pressure area (that is, the glass you stir).    if the orifice is in the center of the glass, then the water will not be moving very quickly, and the pressure will be higher there.  towards the outer edge of the glass, the water will be moving fast, so this will cause a relative decrease in the hydrodynamic pressure.  so, i would reason that the closer the orifice is to the edge of the glass, the greater the movement of the ball.