水波的張力

The surface tension of water at 20 deg.C is 0.07 N/m (Netons per metre)
That is to say, if you treat the water surface as an elastic skin, an imaginary line of 1 metre drawn on the surface will experience a force of 0.07 N acting perpendicularly to it and pulling the line in opposite directions.

2007-07-12 16:46:47 補充：
a typing error in the unit of surface tension, it is [Newtons per metre].