Cloud in a Bottle Demonstration

Use Water Vapor to Form a Cloud

You can make your own cloud in a bottle using a bottle, some warm water, and a match.
You can make your own cloud in a bottle using a bottle, some warm water, and a match. Ian Sanderson / Getty Images

Here's a quick and easy science project you can do: make a cloud inside a bottle. Clouds form when water vapor forms tiny visible droplets. This results from cooling the vapor. It helps to provide particles around which the water can liquefy. In this project, we'll use smoke to help form a cloud.

Cloud in a Bottle Materials

You only need a few basic materials for this science project:

  • 1-liter bottle
  • Warm water
  • Match

Let's Make Clouds

  1. Pour just enough warm water in the bottle to cover the bottom of the container.
  2. Light the match and place the match head inside the bottle.
  3. Allow the bottle to fill with smoke.
  4. Cap the bottle.
  5. Squeeze the bottle really hard a few times. When you release the bottle, you should see the cloud form. It may disappear between "squeezes."

The Other Way to Do It

You can also apply the ideal gas law to make a cloud in a bottle:

PV = nRT, where P is pressure, V is volume, n is number of moles, R is a constant, and T is temperature.

If the amount of gas (as in a closed container) isn't changed, then if you raise the pressure, the only way for the temperature of the gas to be unchanged is by decreasing the container volume proportionally. If you're not sure you can squeeze the bottle hard enough to achieve this (or that it would bounce back) and want a really dense cloud, you can do the not-as-child-friendly version of this demonstration (still pretty safe).

Pour hot water from a coffeemaker into the bottom of the bottle. Instant cloud! (... and a slight melting of the plastic) If you can't find any matches, light a strip of cardboard on fire, insert it into the bottle, and let the bottle get nice and smoky.

How Clouds Form

Molecules of water vapor will bounce around like molecules of other gases unless you give them a reason to stick together.

Cooling the vapor slows the molecules down, so they have less kinetic energy and more time to interact with each other. How do you cool the vapor? When you squeeze the bottle, you compress the gas and increase its temperature. Releasing the container lets the gas expand, which causes its temperature to go down. Real clouds form as warm air rises. As air gets higher, its pressure is reduced. The air expands, which causes it to cool. As it cools below the dew point, water vapor forms the droplets we see as clouds. Smoke acts the same in the atmosphere as it does in the bottle. Other nucleation particles include dust, pollution, dirt, and even bacteria.