OT (but science ...)

I've not heard of it being said about water that's being poured, but I can certainly tell easily by sound when water running from the hot tap, initially cold, starts to run warm. Probably different amounts of dissolved air in the water.

As I don't take milk in coffee, and as I'm a pre-lactarian (milk in cup before tea) for tea, I've never noticed a change in the tinkling.

I have noticed a clear pitch shift up when stirring something into a liquid - say a powdered soup or hot chocolate. You also get a very noticeable effect if you stir honey into tea - the pitch rises as it distributes in the liquid, but if you pause and and just tap the rim of the cup with the spoon, it will then fall. Stir again, and it rises again.

My guess on this phenomenon is because you are changing the amount of damping effect the liquid has on the resonance of the cup. Un-damped the cup will "ring" at its natural frequency. As you add damping you will shift that resonance away from its natural frequency.

(I have seen some explanations for a rise when stirring something without adding or mixing anything - that relate the cut to a resonant tube of air - when the length of column reduces at the sides when the liquid swirls)

I don't know but, if this is instant coffee, always put the milk in first. It takes a bit of stirring to get rid of the lumps but the end result is better. If you put boiling water directly on the granules a lot of the volatiles disperse in a cloud of vapour, which is not really where you want them.

Try it, it's true.

Recently boiled water poured from a kettle has a much "softer" sound IME giving a muted sound with less treble in the "splash" sound.

I don't need to try it - it's how I've made (instant) coffee for

I was thinking something around those ideas.

I wonder if there is some as yet unrealised application ?

I still think it should be possible to deduce liquid flow from pitch if you know the diameter of the pipe and the characteristics of the obstruction you use to generate it. I was thinking this after the hall effect flow sensor needed changing on my boiler.

Piss alarm to catch gents with a poor aim ?.

Are you just using the milk to lower the temperature? I use water at 90 degrees and add the milk after the coffee, but I'll experiment with milk first in a few minutes and report back - an excuse to eat the biscuit that I've been fancying ;-)

I can't remember which way it is, but I was surprised that it was possible over the TV.

Likewise here. I run the kitchen hot tap to waste, listening for the change of note, then swing the tap over to the bowl. I get a more persistent noise, if I should miss the more subtle one - the heat somehow causes the hot tap washer to begin vibrating loudly. I have never bothered to fix it, because it is quite a useful warning.

I've noticed a very obvious change in tone from the mixer shower. It takes about 15 seconds for the hot water to come through, and the change is associated with that. I know to not get in until that change occurs, or it will be a cold shower!

I agree with this - I do the same, and for the same reason

I find it is quite an obvious difference...

In the past I have put the kettle on, gone away for a moment, and come back to pour the water assuming it should have boiled by then. I know immediately when I start pouring, that I must have failed to hit the switch properly!

(I normally remember to check if the kettle feels hot now!)

Density change in the fluid perhaps.

viscosity of near-boiling water is a lot less than water at room temperature. So when poured the hot water is less "sticky" and breaks up into smaller bits.

Well, the biscuit was great but I didn't notice any difference in the coffee

My son always heats the water for coffee to only 70 degrees, saying that's the optimum temperature.

Another factor that might well affect the sound is that the surface tension of boiling water is zero.

John