Tie and Untie Water Streams

By Jitender Singh on Jan 16, 2021

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.

Procedure

Make two 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.

Discussion

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.

Variant: Cohesive and Adhesive Forces of Water

The force between two surfaces of the same material is called cohesive force and that between the surfaces of dissimilar materials is called adhesive force. There are several popular demonstrations of water surfaces attracting each other for cohesive force. There are relatively smaller number of popular demonstrations to show the adhesive force. This experiment gives one such simple demo.

Procedure:

1. Close the two holes by fingers. Fill water in the bottle. Do not put the cap.
2. Remove fingers so that water starts coming out from the holes. You see two streams.
3. Using your thumb and a finger, bring the two streams in contact with each other. Occasionally you will see that the two streams have merged into one. This is due to cohesive force between the two water streams. When do you find the merger more frequent, when the bottle is nearly filled or when a good amount of water has gone out?
4. Put a tape on the upper hole. Fill the bottle and let the stream come out from the open hole. Carefully watch as the stream slows down. The stream starts going along the surface of the bottle. This is due to adhesive force between the plastic surface and the water stream.
5. Repeat above step, but the bottle tilted as shown in the figure. Does water still goes along the surface of the bottle? Write your observations.

Related

1. Surface tension and thirsty coin
2. Sticking slides and adhesive forces

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