Water knots

An empty two-lb. can is pierced five times just above the lower edge with a thin nail. The first hole should be just over an inch from the fifth. Place the tin under a running tap, and a jet will flow from each hole. If you move your finger over the holes, the jets will join together. The water particles are attracted to one another and produce a force acting into the interior of the liquid, the surface tension. It is also this force which holds a water droplet together. In our experiment the force is particularly clear, and it diverts the jets into a sideways are and knots them.