Clouds in a lab

In this video Pete demonstrates how changes in pressure result in cloud formation, using a demijohn bottle, a bicycle pump and ethanol.

Pete pumps air into the sealed jar, increasing the pressure to the point at which the rubber bung is ready to pop from the neck of the demijohn. When the rubber bung is removed, the pressure in the jar drops rapidly and the vapour in the jar condenses to form a cloud.

How do you think the state of the atmosphere in the room you are in – the temperature and humidity –might affect the cloud that forms? We look forward to hearing your thoughts in the Comments area within this Step.