Laminar flow

It seems like a spe­cial ef­fect or a trick, but it's sci­ence!

Safe­ty pre­cau­tions

Per­form these ex­per­i­ments only un­der adult su­per­vi­sion.

Reagents and equip­ment

• glyc­erin;
• food col­or­ing;
• 4 binder clips;
• 2 glass­es with dif­fer­ent di­am­e­ters;
• pipette.

Step-by-step in­struc­tions

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!

Process de­scrip­tion

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.