Instant Clouds: Just Add Pressure!

Time to make Zeus jealous. Mama always told you that you can plan a pretty picnic, but you can't control the weather. Well the forecast today is that your mama is, sadly, 100% wrong. With a little bit of pressure applied, a front of cloudy weather will be moving in to your bottle in less than a microsecond. You can re-create the same process that clouds go through when forming to make your very own pet cloud. There are other methods out there, but I truly prefer this one, and wanted to share it because it's so easy and stunning!

• What: Instant Cloud!
• Concepts: pressure, meteorology, physics, adiabatic process, water cycle
• Materials:
  • Rubber Stopper with no hole (can get at hardware store)
  • Water Bottle (bigger is more fun)
  • Isopropyl Alcohol (99%)
• Tools:
  • Bike pump with sports needle
  • Drill

All right! Let's start clouding around!

You are about to be the master of weather, and with that comes great responsibility. First, gather up the 99% isopropyl alcohol from a pharmacy, your stopper with no hole, and a bike pump.

The reason I use alcohol for this instead of water as some others do is because of the specific scientific process our cloud is about to go through. One of the processes by which clouds are formed is referred to as a adiabatic process, which air goes through as it rises in the atmosphere. As hot air rises and cools, that body of air expands as there is less pressure on it at high altitudes. That is why balloons expand and eventually pop up high.

The large expanding bit of air means that the individual molecules don't bump into each other as much, and that means a drop in overall temperature. This makes the air cool, and as it does so, it eventually falls below the dew point, which is when water vapors start to collect in droves. They often nucleate around particles in the atmosphere, but are basically getting released from high pressure to low pressure and are thus forming! A great write-up can be found here.

We are basically going to put the liquid alcohol under a lot of pressure, and then when the pressure drops the molecules act like springs that have been squished too tight, and they release into the air in vapor form. This works so much better with alcohol because the hydrogen bonding (cohesive force) isn't as tight as with water, so they spring up easier.

KIND CAUTION: Because we are using alcohol, please be careful with flames near the bottle especially as it volatizes. It can turn the whole system into a fiery rocket, which some people intentionally do (and is amazing), but that's a separate experiment to be prepped for. As always, too, be careful when pumping up and releasing big amounts of pressure, especially with students. They can cover their eyes, and most importantly keep a hand on the pump parts so they don't fly up mid-experiment.

Take your rubber stopper and the smallest drill bit you have (we used 1/16"). Make a hole through the middle of your rubber cork, which will serve as a pilot. With a little squeezing and rotating, push the sports needle through. Then attach it to your bike pump, and your cloud plug is all set. You're ready to take on some serious pressure!

Take any labels off your cloud bottle so you can see it clearly. Bottles with sturdy thicker plastic work best for this experiment (often seen in 2 liter bottles). Carefully pour a small amount of isopropyl alcohol into your container (about 1/3 cup should do). Then you're ready to go!

Place your cloud plug into the bottle, and hold it there firmly. If you have a class for a 1.5L bottle, have them count 10 pumps out loud to increase the pressure in the bottle. When you release the plug, a cloud will instantly be formed with a dramatic sound and puff. YAY! A CLOUD!

From there, squeezing the bottle, you can make little cloud rings, or you can place the plug in to fascinatingly see the cloud disappear with the next press of the bike pump. With the same small amount of alcohol, you can repeat this process many, many times, and try out variations. What happens when you pump it less, more, when you try it with water, oil, milk?

Hope you enjoy turning cloudy weather into a good thing. As always, keep exploring and reach out with what you think below!