Rope bridge: pour water from far away

How can you replace a hose with some yarn?

Safe­ty pre­cau­tions

Warn­ing! Only un­der adult su­per­vi­sion.

Equip­ment

  • piece of yarn;
  • glass of wa­ter;
  • emp­ty glass.

Step-by-step in­struc­tions

Soak a piece of yarn in a glass of wa­ter. Press one end of the yarn against the same glass with your fin­ger, and press the oth­er end against an emp­ty glass. Try to pour the wa­ter from one glass to the oth­er as if the yarn were a hose. Not a sin­gle drop spills!

Process de­scrip­tion

Mol­e­cules are at­tract­ed to each oth­er. The fibers of the yarn are thor­ough­ly wet­ted with wa­ter, and it spreads along them: the force of the in­ter­ac­tion be­tween the wa­ter mol­e­cules and the fibers of the yarn is stronger than that of the wa­ter mol­e­cules with each oth­er. In ad­di­tion, this in­ter­ac­tion is also stronger than the in­ter­ac­tion of wa­ter mol­e­cules with air mol­e­cules, which pre­vents the for­ma­tion of wa­ter droplets on the sur­face of the yarn: sur­face ten­sion tends to re­duce the area of con­tact be­tween wa­ter and air. If you try to pour too much wa­ter at once, how­ev­er, grav­i­ty will over­pow­er the sur­face ten­sion and the wa­ter will spill!

A sim­i­lar ex­per­i­ment is in­clud­ed in the MEL Physics sub­scrip­tion!

Try it