Science in Sweatpants: Cloud in a Bottle

For today's installment of Science in Sweatpants we're making our own clouds but before we do, it helps to understand how clouds form in nature. 

All over the world, there are bodies of water that get heated up by the sun's rays. As that water heats up, evaporation takes place. This means water is going from its liquid form to its gas form, water vapor. We're surrounded by that water vapor all the time but we can't see it because it's invisible.

Sometimes that water vapor will rise higher through the atmosphere where it will cool down and condense back into water droplets. 

When billions of these water droplets come together, they form the clouds we see.

There's also another element to cloud formation--cloud condensation nuclei. These can be smoke, dust, pollen, or pollution and act as a nucleus for the water to condense around. 

Now let's get to making our own clouds! (Adult supervision is recommended for both of these demonstrations.

Here's what you'll need for the first cloud:

  • A clear, glass container with its lid
  • Ice cubes
  • Hot water
  • Hairspray

Fill your glass container up about a quarter of the way with the hot water. Turn the container's lid upside-down and stack a few ice cubes onto it. Before you place the lid over the mouth of the jar, spray a small amount of hairspray in the jar. 

After spraying the hairspray, quickly place the lid with ice cubes over the mouth of the jar. After a few moments, you'll notice a cloud form.

When you add the hot water to the jar, it immediately begins evaporating so water vapor is collecting in the jar. The hairspray molecules act as the cloud condensation nuclei for our water droplets to condense around, we just need something to cool down the air in the jar. That's what we're doing by sealing the jar with the ice-holding lid. 

As temperatures inside the jar fall, a cloud forms. When you remove the lid, you can see the cloud escaping. 

For the second cloud you'll need:

  • One 2-liter plastic bottle, emptied and cleaned out
  • Rubbing alcohol
  • Tire pump with a metal inflation needle attachment
  • A rubber stopper or cork with a small hole for the tire pump needle
  • Safety glasses or safety goggles

Start by pouring a small amount of rubbing alcohol into your bottle. Tip the bottle gently so that you can coat the sides of the bottle with rubbing alcohol. 

Now plug the bottle with your stopper and insert the tire pump needle into the stopper so you can begin pressurizing the bottle. 

Give the tire pump 5-10 pumps but before you pull the stopper out, feel the bottle. It should feel hard because we've increased the air pressure inside. As we increased the air pressure, we've also increased the temperature so you may notice the bottle is a bit warmer too. 

Now pull the stopper out and watch what happens! You should notice a cloud form immediately.

That's because pulling the stopper out releases all that air and the pressure drops quickly. As the pressure drops, the temperature drops as well. 

Remember, in nature when the temperature drops enough, water vapor will condense into water droplets. That's exactly what we did inside our bottle atmosphere!