Set up an amazing self-organizing process at your desk!
Warning! Only under adult supervision.
- vegetable oil;
- Petri dish;
Remove some graphite from a pencil and crush it to a fine powder in a mortar. Combine the resulting graphite powder with vegetable oil and stir – you’ve made a rheoscopic liquid! Such a fluid will allow you to visualize currents and trace its movement. Fill a glass to the brim with boiling water, set a Petri dish on the glass, and fill the Petri dish about halfway full with the mixture of oil and graphite. The water vapor heats the Petri dish and, after a while, cells will form on the surface of the oil mixture.
When the lower layers of the liquid become warmer than the ones above them, you’ll be able to observe flows as the warmer layer rises and the colder layer sinks. These flows occur due to the fact that oil’s density decreases as it heats up. Under the influence of gravity, the less dense, warmer layer rises to the surface, and the denser, colder layer sinks. The layer that rises to the surface subsequently cools down, the descending layer heats up, and the movement continues. This phenomenon is called convection, and the currents caused by this process are called convection currents. If you heat a rheoscopic fluid, you can see that convection can break into independent, closed Rayleigh-Benard cells under certain conditions. Mixing occurs independently in each cell, and there is practically no liquid transfer between them.
A similar experiment is included in the MEL Physics subscription!