What happens when people throw boiling water in the air on a cold day?

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What happens when people throw boiling water in the air on a cold day?

You can watch videos on the web, but this is a great experiment to try at home, if you do it carefully and don’t burn yourself! On a day with very cold, dry air, throw a cup of boiling water into the air. Use a sweeping motion that aims the water away from you. The water will break into tiny liquid water droplets, most of which will evaporate before they hit the ground.

Evaporation plays a key role in this fun phenomenon. Evaporation is the transition of water from the liquid phase to the gas phase. The rate of evaporation depends on the temperature difference between the water and the air, and evaporation is more rapid in low humidity. Hot water is closer than cold water to evaporating, so your cup of near-boiling water is already close to becoming a vapor.

By dispersing the liquid water into a collection of liquid water droplets, you’ve increased its surface area, which also speeds evaporation. The combination of hot water, cold, dry air, and high surface area causes most of the tossed near-boiling water to evaporate before it hits the ground, and the tiny droplets that don’t evaporate will freeze into ice crystals while still in the air.

If the water is not hot enough, evaporation will be slower. Instead of evaporating, the liquid will hit the ground first, and then freeze.

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.