Problem M. 263. (October 2005)
M. 263. Fill the washbasin with some water, wait until the water has a smooth surface than (using a rope or a chain) suddenly pull out the plug and let the water drain away. Measure the time while the washbasin is emptied, as a function of the amount of water. Endeavour to investigate both cases: when there is, and there is no whirl in the water.
Deadline expired on 11 November 2005.