This demonstration shows how changes in pressure and temperature can create visible clouds. When air inside a sealed bottle containing rubbing alcohol is compressed and then suddenly released, the vapor condenses into tiny suspended droplets, forming a cloud.

1. Prepare a cork or stopper with a hole through it and insert a ball inflating needle. Add a toothpick sideways to stop the cork from being pushed inside the bottle.
2. Pour about 60 ml of rubbing alcohol into a clean, clear 2 L plastic bottle. Seal with the cork stopper.
3. Tilt and shake the bottle to coat the inside with alcohol.
4. Attach a bicycle pump to the stopper and pump in about four strokes of air.
5. Quickly remove the stopper and observe the cloud forming inside the bottle.
6. To repeat, reseal the bottle, add more air, and release again.
7. Alternatively, twist the bottle to create the pressure rather than using the bicycle pump (as shown in Links)

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• Try with warm water instead of rubbing alcohol (the effect will be less dramatic).
• Compare the speed of cloud formation using different amounts of rubbing alcohol.
• Use a flashlight to shine through the cloud for better visibility.
• Record the cloud with slow-motion video to observe droplet formation more clearly.

• Safety goggles required for everyone nearby.
• Use only a small amount of rubbing alcohol—pour excess back immediately.
• Do not over-pressurize the bottle—too much pressure may cause it to rupture.
• Point the bottle away from people when releasing the stopper, as liquid spray may occur.

• What causes the cloud to form when the stopper is released? (The sudden drop in pressure cools the vapor, causing condensation into tiny droplets.)
• Why do we use rubbing alcohol instead of water? (Alcohol evaporates more easily, producing a more dramatic effect.)
• How is this similar to cloud formation in the sky? (In both cases, rising air cools and water vapor condenses on small particles to form visible droplets.)
• How do temperature and pressure affect the ability of air to hold water vapor? (Warm air holds more vapor; cooling reduces capacity and leads to condensation.)