[jansenwrasse]

Niagra falls is a 160' drop to the water below. How much warmer is the water below than the water on the top of the falls, as a result from transer from potential energy to thermal energy?

Quick ref.
1cal = 4.148J
Gravity = 9.80655m/s^-2

question is from General Chemistry by Linus Pauling.

Good Luck !

[nj_bartel]

You'd need a number for the friction between the water molecules among other things - that's a really intense problem.  Unless you're to assume direct conversion from kinetic energy into temperature?

[P]

Yea I reckon it would be allot more complex than that even.  When the water falls, the PE turns to KE, SOME of which may be transfered to TE through friction when it smashes into the bottom of the fall. I reckon that during the fall though you will loose more water than usual due to vapour and evaporation, which causes cooling.  Therefore at a guess  -  you wouldn't see much in the way of temperature change at all between the top and the bottom of the falls.    ??


However, if this is a question from a text book then there must be some increase. I suppose it wants you to ignore the increased evapouration.

[P]

Actually  -  alot would be lost to sound energy too.   As it falls I think it would loose more thermal energy to the surounding air as the water breaks up into droplets (more surface area) and moves faster through the air (falling).  What the net result in temperature change would be I do not know.

[jansenwrasse]

Way over thinking it

The temp would be just before the water falling hits the river below.

[nj_bartel]

All that information we're taking into account is assuming right before it hits water.

[P]

The temp would be just before the water falling hits the river below.

Then it will actually be colder.  The heating comes from friction generated when the water hits the bottom and the kinetic energy is changed to thermal. As it falls you will get increased evaporation which will cool the water as it falls.   The potential energy is converted to kinetic energy not heat, until it hits the bottom and you get heating from friction.

Anyway - in your opening post you said it was a 160' drop you didn't say "just before it hits the bottom."

Niagra falls is a 160' drop to the water below. How much warmer is the water below than the water on the top of the falls, as a result from transer from potential energy to thermal energy?

SO:  you will get cooling as it drops and then re-heating when it actually hits the bottom.   What the net change would be I do not know.


Did you find out the answer?