To tie and untie water streams
To tie and untie water streams into a single stream.
In everyday life, the phenomenon of taking bath under shower heads is enjoyed by most of the peoples. At that time, you can see separate streams when the valve is fully open but streams cling together when the valve is partially opened.
plastic bottle, nail, water
Punch three small holes about 2 mm apart near the base of the bottle. Pour water and you get three distinct water streams. Using you thumb and index finger, bring the water streams nearer and remove your fingers. The streams stay together. Flick the stream with index finger, they separate.
When brought together, the cohesive forces keep the streams bonded. By flicking, you forcibly separate the water streams. The cohesive forces are not strong enough to bring them together. Closer the holes, easier it is to knot the stream. If the bottle is full, it is difficult to knot the streams but easier to un-knot. Opposite happens when the bottle is almost empty.