How to grow a rainbow at home

Is it pos­si­ble to grow a rain­bow at home with­out lep­rechauns? Learn how with this video!

Safe­ty pre­cau­tions

None.

Equip­ment

• pa­per tow­el;
• wa­ter-based mark­ers;
• wa­ter;
• Petri dish;
• pa­per clip;
• thread.

Step-by-step in­struc­tions

Use some mark­ers to draw the be­gin­nings of a rain­bow on a pa­per tow­el. Use a pa­per clip and some thread to sus­pend the pa­per tow­el above a Petri dish. With the ad­di­tion of wa­ter, your rain­bow be­gins to inch to­wards the sky!

Process de­scrip­tion

A ma­te­ri­al is con­sid­ered “wet­table” if it in­ter­acts with wa­ter more strong­ly than wa­ter mol­e­cules in­ter­act amongst them­selves. Wa­ter strives to max­i­mize con­tact area with a “wet­table” ma­te­ri­al, and spreads out over the sur­face. In our ex­per­i­ment, the wa­ter thus “wets” the pa­per tow­el, but grav­i­ty in­ter­feres with its abil­i­ty to rise through it. How­ev­er, once in the nar­row cap­il­lar­ies of the wet­ted ma­te­ri­al, the wa­ter’s sur­face adopts a con­cave shape, form­ing a menis­cus. Mean­while, the wa­ter pres­sure un­der this menis­cus be­comes low­er than at­mo­spher­ic pres­sure, and the wa­ter be­gins to rise. A pa­per tow­el con­sists of plant fibers that have nu­mer­ous cap­il­lar­ies in their struc­ture that the wa­ter can rise through. The thin­ner the cap­il­lary, the high­er the wa­ter ris­es, try­ing to bal­ance the pres­sure dif­fer­ence. The wa­ter thus moves up­ward through the ma­te­ri­al, lift­ing the dye mol­e­cules with it.