why doesn't the friction caused by flowing water heat the water up?

[BenNicholson]

why doesn't the friction caused by flowing water heat the water up?

Thanks,

Ben Nicholson

[Graham-W]

It does. In my schooldays we were introduced to a "Callender's Drum." this was a metal drum containing water and fitted with a thermometer. On rotating the drum via a crank handle the temperature of the water would rise slowly. This was given as an example if converting mechanical energy into heat energy.
I've had a quick Google for "Callender's Drum" and find very little information. Is my memory finally going? ps. It's 40yrs since I did physics so it may be different now.

[ChuckFickens]

as graham says, it does.

http://en.wikipedia.o...al_equivalent_of_heat

[Graham-W]

Thanks Chuck. Was beginning to think I had finally lost the plot.

[joggerjayne]

So if your bath water is going cold ...

... you can warm it up by swirling it around ... ?

[Teddio]

It Does. By the way Callender's apparatus heats up a metal drum, containing water, by friction.

[mollykins]

how long and how big a force would you have to use to heat up bath water, from luke warm to whatever temperature is considered a hot bath?

[Panic Button]

Bath getting cold?

Do something vigorous.

[Bert]

It's not quite the same thing, but I think it was Joule who measured the temperature of the water at the top and bottom of a waterfall, and found that it was warmer at the bottom because the kinetic energy of the water was converted to heat energy. We did a similar experiment at school (45 years ago). We had a tube made of good insulating material (I'm pretty sure it was a length asbestos drain-pipe!) about two metres long. We had some lead shot, which we put into the tube, then sealed both ends. We inverted the tube many times, then opened it and measured the temperature rise of the lead shot. Knowing how many times we had inverted the tube, we knew the total distance fallen by the shote, and so worked aut a value for the mechanical equivalent of heat.

[Bert]

I've never heard of Callender's Drum. Isn't that diagram in the link that Chuck gave a diagram of Joule's apparatus?
If Ben's question is wondering why rivers aren't hotter the further downstream you measure the temperature, or why the cold water that comes into your house isn't warm by the time it gushes out of the tap, it's simply because the theoretical temperature rise is very small and there are so many ways for the heat generated by the friction to be lost - to the riverbank and to the air, or through the copper pipes in your house.

[Bert]

I googled "callender's drum" and got nothing. However, when I googled "mechanical equivalent of heat" and 'callender' I got 17,000 hits. One (15th) was to finegroup, and an apparatus that looks mechanical, and is attributed to 'Calendar' (sic). The first two hits refer to a scientist working at about the right time named Callendar (sic). But the references refer to a method involving heating water electrically. The fifth hit refers to a "Callender (sic)-and-Barnes calorimeter, which again involves heating water by electicity. I hope this may be of some help.

[Teddio]

Calculations on the conversion of Gravitational Potential Energy to Heat Energy by a waterfall are largely pointless are there are too many variables. For instance the temperature and relative humidity would be just two factors in the rate of evaporation of the falling water. Approx 2.2 Megajoules of heat energy would be "lost" changing the state of the water from liquid to gas (vapour)

[Bert]

You're right, Teddio. That's what Joule found:
Joule married Amelia Grimes on 18 August and the couple went on honeymoon. Marital enthusiasm notwithstanding, Joule and Thomson arranged to attempt an experiment a few days later to measure the temperature difference between the top and bottom of the Cascade de Sallanches waterfall, though this subsequently proved impractical. (Wiki)
It doesn't say why it's impractical, but your suggestion is probably just one of the reasons.
[Latent heat of vaporisation of water at boiling point: 2.256 MJ/kg.]

[Peter Pedant]

Bit of a late answer:
Teddio is wrong and Graham right. There is a OU prog on this, s101 or t101, and they use a hydroelectric plant in Wales - the one where you can pump water up the hill and then let it down. There can only be one.

Callender's drum - uses friction from a belt, and it had that cute thermometer with an s bend in the middle
and so did Count Rumford's cannon boring expt - a cannon boring thing in a cannon

which is not really what the q is all about:

Viscous drag during laminar flow should be dissipated as heat.

So the answer to Ben N's question is, yes we all think it does, but the effect is small.