Does falling water chill due to losing gravitational energy?

Quote: Wizard

Okay, I think we can all buy that. When water falls over the waterfall it makes a lot of noise and causes spray when it hits the bottom. I would call that gravitational energy converting to kinetic energy.

Let me rephrase the question this way. If there were a waterfall in a vacuum, to tease out the effect of air friction, would the water cool down half way down?

p.s. Welcome to the forum! Hope you'll stick around.

Quote: 1nickelmiracle

Make a bath too hot and collect and dump water back and feel the water cool quickly. Wouldn't work without the air to interact with such as in a tube.

Quote: Doc

I have only scanned the thread, but the comments by Face and ChesterDog seem to cover the topic rather well. My summary would be this:

(1) If we were to neglect evaporation and frictional effects from the atmosphere, the potential energy of the water at the top of the falls would be converted to kinetic energy during the fall, with no reason to expect a temperature change during the fall.

(2) Upon impact, the kinetic energy would be converted primarily to internal energy, resulting in a temperature increase. This is the 0.1 degree temperature rise that was discussed in the article linked very early in the thread.

(3) If we added on just the effect of viscous drag due to the presence of the air, I think the primary change would be that the kinetic energy would be converted partially to internal energy during the fall, giving a gradual and extremely small temperature rise during the fall, followed by most of the 0.1 degree temperature rise after impact with the pool at the bottom.

(4) On the other hand, I highly suspect that the primary factor in temperature change really is the evaporation. Even if only a very small portion of the water evaporates during the fall, the conversion from liquid to vapor will require a significant input of heat. Some of that will come from the surrounding air, and some will come from the water that does not evaporate. Both the air and the liquid water will be cooled, and I highly suspect that this cooling will substantially overbalance the heating due to conversion of potential energy to kinetic energy to internal energy.

(5) If somehow this were to happen in a vacuum, there would be no viscous interaction with the atmosphere, but there would still be evaporation. In fact, in the vacuum the water would evaporate much more readily, giving even more cooling.

Quote: AZDuffman

A quick google search yielded this..

Quote: Pacomartin

Quote: AZDuffman

A quick google search yielded this..

This earlier post from the 1941 textbook says the water temperature increases.

I just started reading Linus Pauling's "General Chemistry" and the first example confuses me. He writes:

Example 1-1. Niagara Falls (Horseshoe) is 160 feet high. How much warmer is the water at the bottom than at the top, as the result of the conversion of potential energy into thermal energy? The standard acceleration of gravity is 9.80665 m s−2.

Solution. The gravitational force on a mass of 1 kg at the earth's surface is 9.80665 N.
The change is [sic] potential energy of 1 kg over a vertical distance h (in meters) is 9.80665 × h J.
In this problem h has the value 0.3048 × 160 = 48.77 m (conversion factor from Appendix I);
hence the change in potential energy produces 9.80665 × 48.77 = 478 J to thermal energy.
The energy required to raise the temperature of 1 kg of water by 1∘C is given above as 1 kcal = 4.184 kJ = 4184 J.
Hence the increase in temperature of the water is 478/4184 = 0.114∘C.

Quote: Nareed

The gravitational attraction between a drop of water and the Earth increases as it falls closer to the surface.

Quote:

If water cooled down as it falls, due to some loss of "gravitational energy," all rain would fall as ice.

Quote: Wizard

While looking at a waterfall in New Zealand somebody said that that water temperature goes down after falling down the waterfall because it loses potential gravitational energy. Is this true?

Quote: Energy Generation and Storage Using Water

Electricity generation using water
As the falling water collides with the bulk of the water at the bottom of the waterfall, water splashes randomly and chaotically in all directions. Part of the kinetic energy gained by the falling water is now converted into the kinetic energy of random motion. As a result, the internal energy of the water increases, and the water temperature rises at the bottom of the falls. It is said that in the 19th century, the famous scientist James Joule first attempted to measure the temperature change of water at a waterfall. His contribution towards the discovery of conservation of energy resulted in the unit of energy joule being named after him.