Fleetie wrote:
> I have noticed in the bathroom, that when I turn on the hot tap in the
> porcelain wash basin, I can tell when the water has started to warm up by
> the change in the sound of the water hitting the basin. The hot water
> sounds very different falling on the porcelain from the cold water. I am
> pretty sure the flow rate is the same or at least, that there's negligible
> difference.

	I have noticed that all my life.

> The cold water seems to be noisier and make more of a "splashing" sound.

	I have noticed mainly the the spectrum of the noise emitted by the tap 
slews downward, perhaps at least one octave, as the warmer water is 
purveyed. The velocity of sound in pipes and in the water does not 
change nearly as much. My pet theory has been that dissolved air (oxygen 
and nitrogen) in the water is more readily formed into bubbles as the 
temperature rises. Certainly said bubble formation will occur at the 
point of throttled pressure release within the partly open valve. The 
presence of bubbles in water significantly reduces the velocity of 
sound, via the reduced bulk modulus of that water mixture. That reduced 
bulk modulus also reduces the modal vibration frequencies (eigenmodes) 
of that pipe/valve fixture/liquid/bubble mixture assembly. Sound 
radiation is often a maximum at such modal frequencies.

Just my opinion.

> Any ideas why? Different surface tension at different temperatures, causing
> the cohesiveness of the drops to be different, and thereby making them break
> up in a different way when they hit the solid surface?

	Pouring warm water definitely emits a lower frequency spectrum as 
compared to cold water. In that case, again, the vapor pressure of the 
water mixture rises with temperature. The vibration frequency spectrum 
of the impacting water globules will vary with the forces such globules 
can impart... I suspect that such forces, likely compromised by 
cavitation enhanced at warmer temperatures, will also experience lesser 
forces.... again lowering the eigenmodal frequencies, etc.  again, my 
offhand opinion.


	Angelo Campanella