Rope bridge: pour water from far away
How can you replace a hose with some yarn?
Warning! Only under adult supervision.
- piece of yarn;
- glass of water;
- empty glass.
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!
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!