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Silly plumbing (or maybe physics) question Malcolm Hoar 01-11-2007
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Posted by Malcolm Hoar on January 11, 2007, 1:44 pm


My bathtub is located some distance from the water heater.
I turn on the hot faucet only and wait. The tub starts to
fill, with cold water initially. After a while, the water
becomes hot. That's all fine and as expected.

However, I can tell when the water is hot by *listening*
to the flow. The sound of the water changes quite significantly
and I've been trying to figure out why.

Clearly, the hot water will be slightly less dense than
the cold but I have a hard time imagining this would
cause an audible change in the sound. Also the metal
faucet will expand and that might change the sound of
the water whistling through the valve. Again, it's
hard imagine the thermal expansion of fractions of a
millimeter causing such an audible effect -- think
about the size of changes between two notes on a piano,
guitar, flute or whatever.

This happens in my current home but I have a vague
feeling I've seen (heard) the effect at other homes too.

Any other theories/inputs? Anyone else even observed
this effect?

--
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|
| Malcolm Hoar "The more I practice, the luckier I get". |
| malch@malch.com Gary Player. |
| http://www.malch.com/ Shpx gur PQN. |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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Posted by avid_hiker on January 11, 2007, 1:51 pm



Malcolm Hoar wrote:
>
> However, I can tell when the water is hot by *listening*
> to the flow. The sound of the water changes quite significantly
> and I've been trying to figure out why.
>
> Any other theories/inputs? Anyone else even observed
> this effect?
>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Would you have well water? After filling for a while, would you be
hearing more water pressure when the well pump kicks in? Do you get the
same sound with just the hot water running?...cold water off.


Posted by Pason on January 11, 2007, 2:06 pm


avid_hiker wrote:
> Malcolm Hoar wrote:
>
>>However, I can tell when the water is hot by *listening*
>>to the flow. The sound of the water changes quite significantly
>>and I've been trying to figure out why.
>>
>>Any other theories/inputs? Anyone else even observed
>>this effect?
>>
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
> Would you have well water? After filling for a while, would you be
> hearing more water pressure when the well pump kicks in? Do you get the
> same sound with just the hot water running?...cold water off.
>


Have you every noticed how the pitch changes when you stir sugar into
your coffee?

Posted by Malcolm Hoar on January 11, 2007, 2:18 pm


>avid_hiker wrote:
>> Malcolm Hoar wrote:
>>
>>>However, I can tell when the water is hot by *listening*
>>>to the flow. The sound of the water changes quite significantly
>>>and I've been trying to figure out why.
>>>
>>>Any other theories/inputs? Anyone else even observed
>>>this effect?
>>
>> Would you have well water? After filling for a while, would you be
>> hearing more water pressure when the well pump kicks in? Do you get the
>> same sound with just the hot water running?...cold water off.
>
>
>Have you every noticed how the pitch changes when you stir sugar into
>your coffee?

No, I only add coffee to my coffee ;-)

But I suspect you're describing a different manifestation
of the same effect. If so, the change is likely in the
reverse direction because I presume the sugar would make
the coffee more dense.

Your data suggests the effect is indeed density related I
think.

--
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|
| Malcolm Hoar "The more I practice, the luckier I get". |
| malch@malch.com Gary Player. |
| http://www.malch.com/ Shpx gur PQN. |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Posted by Malcolm Hoar on January 11, 2007, 2:11 pm


>
>Malcolm Hoar wrote:
>>
>> However, I can tell when the water is hot by *listening*
>> to the flow. The sound of the water changes quite significantly
>> and I've been trying to figure out why.
>>
>> Any other theories/inputs? Anyone else even observed
>> this effect?
>>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
>Would you have well water? After filling for a while, would you be
>hearing more water pressure when the well pump kicks in? Do you get the
>same sound with just the hot water running?...cold water off.

No well (or pumps) here. Regular city water supply.

I've generally noticed it with the hot faucet full on and
the cold faucet off.

--
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|
| Malcolm Hoar "The more I practice, the luckier I get". |
| malch@malch.com Gary Player. |
| http://www.malch.com/ Shpx gur PQN. |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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