219) A flow is called sonic, if the Mach number is unity.

220) An error of 1% in measuring head over the crest of the notch (H) will produce an error of __________ in discharge over a triangular notch,

221) A flow through a long pipe at decreasing rate is called __________ uniform flow.

222) The surface tension of mercury at normal temperature is __________ that of water.

223) The property of a liquid which enables it to resist tensile stress is called its surface tension.