The Science of Shaving Cream Clouds

In this experiment, the shaving cream represents a cloud and the food colouring represents water vapour. Food colouring is denser than both shaving cream and water; as it moves through the foam, it eventually becomes too heavy for the “cloud” to hold, acting just like rain!

Rain is a form of precipitation. This occurs when water vapour in a cloud condenses to form drops large enough to fall. Precipitation can take many forms: rain, drizzle, hail, snow, and sleet. It is all determined by relative humidity, which is the amount of water in the air compared to what the air can actually hold at that specific temperature.

• Temperature Rise: If the temperature goes up but the amount of water stays the same, the relative humidity falls (the air has more “room” for water).
• Temperature Fall: If the temperature drops, the relative humidity rises. If it drops past the dew point, the air becomes saturated and the water must condense into liquid droplets.

If the air is cold enough (below freezing), these droplets will freeze and fall as snow or sleet. Rain is a vital part of the water cycle, where water evaporates from oceans and lakes, forms clouds, and eventually falls back to Earth to begin the process all over again.

Variables to test

Find out more on variables here.

• Density Comparison
  Try using different food colours. Do some “rain” faster than others?
• Liquid Substrates
  If you place shaving cream on another liquid such as canola oil or glycerine, does the experiment still work? Consider how the density of the bottom liquid affects how the “rain” falls.
• Foam Structure
  Can you use a different foam on top of the water, such as soap foam or even whipped “aquafaba” (pea foam)? How does the bubble size in the foam change the way the dye travels?