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Science Sundays: How Clouds Form

Posted at 6:00 AM, Aug 07, 2022
and last updated 2022-08-07 09:00:47-04

BAKERSFIELD, Calif. (KERO) — In this edition of Science Sunday, we’re going to be learning how clouds form, and the best way to do that is to make one for ourselves!

Items needed:

  • One clear two-liter bottle 
  • Rubbing alcohol 
  • One 0.625” valve stem 
  • One bicycle pump  


  1. Add a small amount of rubbing alcohol to a two-liter bottle. 
  2. Cap the bottle with the valve stem (it will be a very snug fit). 
  3. Swirl the alcohol to release vapors into the bottle. 
  4. Attach the valve stem to the pump and pump it 2-3 times. 
  5. Pull the valve stem out!

Once you pull out the valve stem a cloud will instantly form in the bottle! That’s because once the stem is pulled the pressure quickly drops and the air inside the bottle expands. This causes the air to cool and become saturated, forming a cloud.

This is essentially what happens in nature, too. Warm air near the ground rises, and is rises it expands. The expanding air cools, and eventually cools enough that the water vapor in the air condenses, and a cloud forms.

Another nice thing about this experiment is that it works in reverse. Once you’ve got a cloud in the bottle you can put the valve stem back in and pump, and the cloud will disappear. That’s because were compressing and warming the air inside to the point that it’s no longer saturated.