Underwater waterfalls: upward and downward flow

How can you make a waterfall underwater?

Equipment: large container of water, two empty bottles, red and blue food coloring, two rubber stoppers, double-sided tape, two empty glasses.

Fill a bottle with hot water and tint the water red. Fill a second bottle with cold water and tint the water blue. Сlose the bottles with rubber stoppers and use double-sided tape to fix each bottle in a glass. Carefully place the glasses in a container of water and carefully remove the stoppers from the bottles. Observe as the cold (blue) water sinks and the hot (red) water rises!

If a solid body is less dense than water, buoyant force will cause it to float on the water’s surface. This is true for liquids as well! Water does not have a single, constant density – over a wide range of temperatures, the warmer water is, the lower its density, and vice versa. Therefore, hot water rises, and cold water sinks. The phenomenon when streams form due to temperature differences is called convection.

A similar experiment is included in the MEL Physics subscription!

Warning! Only under adult supervision.