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Cloud in a Bottle

Have you ever wondered how clouds form?

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Have you ever wondered how clouds form? Moist air rises in the atmosphere, cools, and water droplets form into clouds. Making your own cloud is a popular experiment in many science books, but it can be a little tricky. Sometimes the results are a little hard to see, but practice always makes perfect.

  • 1-liter clear plastic bottle with cap
  • Foot pump with rubber stopper attached
  • Water
  • Rubbing alcohol
  • Safety glasses
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Click here to watch the video!



Adult supervision is required!

  1. Put on your safety glasses and start by pouring just enough warm water in the bottle to cover the bottom.
  2. Swirl the water around and then put the rubber stopper in the bottle.
  3. Start by pumping the foot pump five times. You will notice that as you start to pump, the rubber stopper will want to pop right out. Hold it in the bottle tightly, being very careful not to let it fly out of the bottle.
  4. After five pumps, pull the stopper out of the bottle. You'll likely see a very faint "poof" of a cloud. There wasn't enough pressure in the bottle to make a good cloud, but now you are starting to get the feel of the foot pump.
  5. Repeat the experiment again, but instead of five pumps, pump the foot pump ten times. You'll notice that the more you pump, the harder it is to keep the stopper in the bottle. Just remember to hold it in there tightly. When you are done pumping, pull out the stopper. You should see a slightly more visible cloud this time.
  6. Now that you have a good feel for how the experiment works, fill the bottom of the bottle again and pump the foot pump 15-20 times. You want to put about 9 kg (20 lbs) of pressure in the bottle.
  7. When you remove the rubber stopper, you should see a good cloud.

Okay, so you've mastered the technique and you're ready for an even better cloud? Make sure you are still wearing your safety glasses. Place just a few drops of rubbing alcohol in the bottom of the 1-liter bottle. Swirl the alcohol around in the bottle, making sure to coat the sides. Then put the rubber stopper in the bottle. Follow steps 3-7 above to make a more visible (and more impressive) cloud.

How Does It Work?

Even though we don't see them, water molecules are in the air all around us. These airborne water molecules are called water vapor. When the molecules are bouncing around in the atmosphere, they don't normally stick together.

Pumping the bottle forces the molecules to squeeze together or compress. Releasing the pressure allows the air to expand, and in doing so, the temperature of the air becomes cooler. This cooling process allows the molecules to stick together - or condense - more easily, forming tiny droplets. Clouds are nothing more than groups of tiny water droplets!

The reason the rubbing alcohol forms a more visible cloud is because alcohol evaporates more quickly than water. Alcohol molecules have weaker bonds than water molecules, so they let go of each other more easily. Since there are more evaporated alcohol molecules in the bottle, there are also more molecules able to condense. This is why you can see the alcohol cloud more clearly than the water cloud.

Clouds on Earth form when warm air rises and its pressure is reduced. The air expands and cools, and clouds form as the temperature drops below the dew point. Invisible particles in the air in the form of pollution, smoke, dust or even tiny particles of dirt help form a nucleus on which the water molecules can attach.

Additional Info

Meteorologists young and old will marvel at our selection of scientific weather supplies.

Sources for this information included the Exploratorium website and the National Hands-on Science Institute.

Customer Reviews

Super Great Thx Review by Jose Ruiz

Thx so much the valve was so cheap and i found a bottle at a store for free. This helped me with a science project and helped me get 2nd place. Thx so much and I love the experiments you do.

(Posted on November 30, 2009)

Cool Review by Ryan Soh

This is Real COOL and i am gonna use this experiment for my assignment thx :)

(Posted on January 9, 2010)

Best experiment ever Review by Julian Lewis

This experiment was the best ever it really helps u understand how clouds are made and formed

(Posted on May 15, 2011)

Cloud in a Bottle Review by David

Very cool! I stumbled upon this myself. in science club we made water rockets for fun and while pumping them full of air, we filled one untill it was nearly impossible to pump more air in and once we picked up the rocket after launch, there was water vapor in it :) very cool

(Posted on January 26, 2010)

amazing Review by natalie gale

its great! everyone was amazed.

(Posted on September 14, 2009)

Not enough information Review by Sarah A

This experiment in the video segment looks great, but I cant find this valve anywhere. More information would be helpful. ALso the video doesn't match the written instructions.

We'll definitely look into that in the near future and try to make the Cloud in a Bottle more accurate. Thank you for the feedback.
-Spangler Science Customer Service Team

(Posted on March 16, 2010)

Question Review by Jane Doe

Where can I get that valve? I live in Hong Kong.

(Posted on November 10, 2009)

Super Cool Review by shoraina

Great Experiment for a science fair project!

(Posted on January 14, 2012)

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