Beeless honeycomb

Safe­ty pre­cau­tions

Warn­ing! Only un­der adult su­per­vi­sion.

Equip­ment

• pen­cil;
• veg­etable oil;
• Petri dish;
• mor­tar;
• glass.

Step-by-step in­struc­tions

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.

Process de­scrip­tion

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!