Cloud in a Bottle
Making a cloud inside a bottle may help you figure out how they form outside in the sky.
Warm, moist air rises in the atmosphere, cools, and beautiful, puffy clouds can be the result. Tiny water droplets become clouds of many different kinds at many different altitudes depending on the conditions. Making your own cloud in a bottle is a popular activity in many science books but it can be a little tricky to pull off. Sometimes the results can be hard to see but practice makes perfect. It also helps to use some ingredients other than water, too.
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Let’s start with making the easy cloud first and then you’ll know what to do for the tougher version. Wear safety glasses and pour a little alcohol into the bottle so it puddles in the bottom.
Swirl the alcohol around inside the bottle. Make sure it coats the lower sides of the bottle.
NOTE: The metal inflation tube needs to go through the stopper. From the bottom of the stopper, drill a hole through the center of the stopper that’s a little smaller than the inflation tube. The tube should slide easily through the stopper from the top to the bottom but still be tight enough to seal the air inside the bottle. The tip of the tube goes inside the bottle and the pump connection goes outside. Attach the pump to the inflation tube.
Insert the stopper into the bottle and pump eight to ten times. As you start to pump, you’ll notice that the stopper wants to pop out. Hold it tightly in the bottle opening so it doesn’t. It may be stronger than you think!
When you’re ready, quickly remove the stopper and watch the cloud form almost instantly in the bottle. If the cloud is faint or just a small puff of one, you’ll need to add more pressure in the bottle before you pop the stopper.
How Does It Work
Even though you can’t see them (even when it’s raining), water molecules are in the air all around you. These invisible, airborne water molecules are called water vapor. When water vapor is bouncing around in the atmosphere, it has a lot of motion energy and doesn’t normally stick together.
Pumping air into the bottle forces water vapor to squeeze together or to compress. Releasing the pressure quickly allows the air in the bottle to expand quickly. In doing so, the temperature of the air in the bottle becomes slightly cooler. This cooling allows the water vapor to stick together – or condense – more easily, and form tiny droplets. Clouds are nothing more than gazillions of groups of tiny water droplets! By the way, rubbing alcohol forms a more visible cloud because alcohol evaporates faster than water. Alcohol molecules have weaker bonds between them than water molecules so they let go of each other easily. As a result, there are more evaporated alcohol molecules in the bottle that are able to condense at a lower pressure. That’s why you see the alcohol cloud more clearly than the water vapor cloud earlier on in the pumping process.
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, become a nucleus on which the water molecules can attach themselves and go from invisible to visible as a cloud.
Take It Further
1. Now you have a good idea what to expect when you’re making a cloud and it’s time to be more realistic. Put on your safety glasses and pour enough warm water into the bottle to cover the bottom. You want more water than you had alcohol.
2. As before, swirl the water around to coat the sides and put the rubber stopper into the opening.
3. Pump about five times. Hang on to the stopper!
4. After five pumps, pull the stopper out of the bottle. You may see a very faint “poof” of a cloud. There probably wasn’t enough pressure in the bottle to make a really good cloud – yet.
5. Repeat the pumping but instead of five pumps, go for ten. You’ll notice that the more you pump, the harder it is to keep the stopper in the bottle. (OK, say it together: Duh!) Pull out the stopper and you may see a slightly more visible cloud this time.
6. See where this is going? Fill the bottom of the bottle with warm water again and pump about 15-20 times. You want to put about 20 psi (103 cmHg) of pressure in the bottle.
7. When you remove the rubber stopper, you should see a pretty good cloud this time. Yes, it’s more difficult to make a cloud using water than alcohol. Give some thought as to why that’s true.
Sources for this information included the Exploratorium website and the National Hands-on Science Institute.