How to make fluid flow in layers
It seems like a special effect or a trick, but it's science!
Perform these experiments only under adult supervision.
Reagents and equipment
- food coloring;
- 4 binder clips;
- 2 glasses with different diameters;
Pour some glycerin into a glass with a larger diameter and insert a glass with a smaller diameter. Steady the glass with 4 binder clips, then use a pipette to inject food coloring solutions (food coloring diluted in glycerol) into the cavity between the glasses. Twist the smaller glass in one complete rotation while gently steadying the larger glass with your other hand. Note that the dyes are mixed. Then twist the smaller glass in the opposite direction – the dyes return to their original, unmixed state!
As you turn the smaller glass, the glycerin moves in what is known as laminar motion. Laminar motion is the movement of a liquid or gas in non-mixing layers. Laminar flow usually occurs when the fluid in question is very viscous or flows very slowly. Glycerin is almost 1,500 times more viscous than water at room temperature. Thus, when the glass is turned, each dye remains in its layer, and the illusion of mixing arises due to the fact that our eyes can’t distinguish between the several colored layers.