Materials Required
  • An empty plastic bottle

How to do it

  • Make three small holes in one of the sides near the bottom of the bottle about 1/2 cm away from each other. The holes should like on the same height.
  • Fill the bottle full with water and ask the child to observe the water streams coming out of the holes.
  • Bring the streams together with the fingers to make it one big stream. Seperate the streams by pushing one finger through the middle of the large stream.

Explanation

  • The closer the holes are placed in the bottle, it is easier to get a whole stream out of  it, but it is harder to seperate it into three seperate streams.
  • The farther the holes are, the harder to bring the separate streams together.
  • It is because of the cohesive forces between the water molecules that keep the streams together.
  • The fuller the bottle, the larger the pressure and the easier to obtain seperate streams.
  • With less water in the bottle, we will get lower water pressure and thus an easier cohesive whole stream.