September/October 2017 – Vol. 30 No. 1

President’s Pick: Cloud in a Bottle

Posted: Monday, August 1st, 2011

by Rick Pomeroy

Purpose: The purpose of this activity is to model cloud formation in a 2 liter clear, colorless soda bottle through the process of adiabatic cooling.

Content: Clouds form in the atmosphere when the amount of water vapor that the air can hold exceeds the capacity.  When the capacity of the air to hold the water is exceeded, water molecules condense on small particles to form clouds.  Various factors affect the capacity of the air, primarily temperature and pressure. Most people have witnessed the condensation of water vapor due to drops in temperature (fog on car windows is an example) however few ever realize that as pressure drops, the capacity of the air to hold water in vapor form decreases.  This factor accounts for the formation of summer thunder head clouds near mountains.
For instance, in July when warm moist air from the Sacramento Valley rises over the Sierra Nevada, it condenses into ice crystals that appear as clouds.  This is largely due to the decreased pressures at high elevations as well as cooling.

Materials

2 liter soda bottle- clear, colorless, with label removed plus cap

Matches, incense, or chalk dust (source of dust or smoke)

Warm water (30 ml per bottle) water does not have to be hot.

Procedure

  1. Put small amount of warm water in the 2 liter bottle (it should barely cover the bottom)
  2. Attach the cap and shake or swirl the bottle to encourage the spread of water vapor throughout the inside.
  3. Strike a match (Incense can be used instead of burning matches)
  4. Remove the cap, blow out the match and drop the extinguished match into the bottle so that some of the smoke enters the bottle at the same time. (chalk dust can be used instead of matches)
  5. Attach the cap firmly
  6. Squeeze the bottle then release quickly so that you hear a pop sound.
  7. Repeat this step several times.
  8. Look inside the bottle and watch for fog to form when the squeeze is released.
  9. It might be helpful to shine a flashlight through the bottle to facilitate seeing the cloud.

Questions

  1. What is the purpose of the smoke or chalk dust?
  2. What would happen if you tried this without the smoke/dust?
  3. Where have you seen  cloud formation caused by decreases in pressure besides in your bottle and over mountains in the summer?

Rick Pomeroy is science education lecturer/supervisor in the School of Education, University of California, Davis and is CSTA’s president.

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Written by Rick Pomeroy

Rick Pomeroy

Rick Pomeroy is science education lecturer/supervisor in the School of Education, University of California Davis and is a past-president of CSTA.

2 Responses

  1. A great meteorology activity. I have done it with a bicycle pump and a stopper to build up pressure and then quickly release it.

  2. This is really cool! I will use the idea when demonstrating changes of state (from liquid to a gas).

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