Why are there sudden changes of temperature when you’re walking near a running body of water?


Why are there sudden changes of temperature when you’re walking near a running body of water?

In: Earth Science


Evaporation is happening near the body of water. That is water molecules going from an ordered state in the water to a more chaotic state. That change in organization results in a change in temperature.

By the equation of thermodynamics, change in temperature (dT) is inversely proportional to the change in entropy (dH).

Evaporation takes away heat energy from the surroundings. So the water is sucking up energy, causing the surrounding temperature to fall.

In a still body of water, the warm water rises to the top. This layer of warm water doesn’t absorb that much heat before it evaporates. In a moving body of water, this layer gets mixed up, bringing cooler water up to the top, which can absorb more heat to evaporate. This is why the area near a moving body of water feels cooler than a still body of water.

Running bodies of water tend to disturb water from its liquid form into little water vapors. When water turns into vapor, it cools the air around it. This is called evaporative cooling.

Evaporative cooling is the reason you feel cooler when you sweat. So how does this work?
Sweat is made of water –two hydrogen atoms and one oxygen atom. Water molecules are good friends, and they like to hang onto one another. They do so when the hydrogen atom of one water molecule hangs onto the oxygen atom of another. When enough of these friends hang out together, you have liquid water.

When large bodies of liquid water are disturbed or heated by the surrounding air, the water molecules get so excited they can no longer hang onto their pals. The more energetic ones break free from the bigger group, grabbing the ones with similar amounts of energy with them. This repeats, and they form smaller and smaller groups of water. When the groups are small enough, they escape into the air and turn into water vapor.
This is where the magic happens. See, whenever the energetic guys break from their friends, they leave the less energetic friends behind. When enough high energy guys leave, the larger group to becomes less and less energetic, making them more and more chill. Same thing happens in the air, as this process repeats with the water vapor that already exists in the air. This makes the air more and more chill.

Now with evaporative cooling causing air to be chiller, the wilder air tends to push and shove its way into the chiller air, which is what causes air movement (wind). All these things combine to make the sea breeze, and SUPER chill times on the beach with a Corona. Kind of makes me yearn for a vaction now when instead, I’m stuck at home explaining evaporative cooling on the internet. Man I can’t wait for COVID to be over… Anyways, I digress.