Cloud in a bottle

This activity is part of our Science Lab series. Check out the ANU Science Lab for more experiments! In this activity, you will construct a cloud in a bottle to explore atmospheric pressure, temperature changes, and condensation nuclei. Watch the video above to see how it is done.

Cloud in a bottle materials & ingredients

• Clear plastic bottle with cap
• Warm or room temperature water
• Matches 

Safety Note: An adult must assist when using matches.

How to make a cloud in a bottle: Step-by-step instructions

Step 1: Add water and smoke

1. Pour warm water about half way up your clear plastic bottle.
2. An adult should light a match, drop it into the bottle, and immediately screw the cap on tightly. The smoke provides tiny floating ash particles that act as condensation nuclei.

Step 2: Squeeze and release

1. Squeeze the bottle: Squeeze the sides of the bottle firmly with both hands. Notice how the inside clears as the pressure and temperature rise.
2. Release the bottle: Quickly let go of the bottle. Watch as a visible cloud forms inside as the air pressure drops and water vapour condenses around the smoke particles.
3. Repeat the squeezing and releasing process to see the cloud disappear and reappear.

How a cloud in a bottle works: The science explained

This experiment demonstrates condensation, adiabatic cooling, and cloud formation:

• Temperature and pressure changes: Squeezing the bottle raises the internal air pressure and temperature, keeping the water invisible in its gas state (water vapour). Letting go releases the pressure, causing the temperature to drop rapidly.
• Condensation nuclei: As the air inside cools down, the invisible water vapour condenses into tiny liquid water droplets. However, these droplets can only form if there are floating solid particles, known as condensation nuclei, to cling to.
• Real cloud formation: In Earth's atmosphere, real clouds form when warm air rises, expands, and cools down. Water vapour in the air clings to tiny airborne particles such as dust, sea salt, or pollution to create the clouds we see in the sky.

Science fair projects & taking it further: Experimenting with variables

• Bottle size: Try creating a cloud inside a large 2 litre bottle versus a small 500 mL bottle. Does bottle volume affect cloud density?
• Water temperature: Compare using cold water from the fridge against warm tap water. Which temperature produces a thicker cloud?

Enjoyed this experiment? Explore more hands-on activities on the Science Lab ANU YouTube channel.