Water level in modified "U" tube | English

Level of liquids in a U-shaped tube to understand pressure is a very routine experiment in fluid dynamics. In this version of modified U-tube, we will look at how the water levels in various parts of the tube differ from each other and what is the explanation for it.

The water level in two arms of the U shaped tube is usually at the same level if the tube is open and both arms are under the same pressure. In this version, the tube is modified in a W-like shape. The central part of the tube is at a slightly higher height and all turns are curved and not sharp to avoid bending of the tube.

When you start pouring water in this modified tube, up to certain level water rises equally in two arms of one half. This is because the same atmospheric pressure is acting on both water columns. If you pour more water into the tube, the water will cross the middle section and start accumulating in the bottom of the second arm and create an air gap as seen in the video. The level in the second big arm is very much lower than the first arm. Adding more water does not increase the level in the second arm anymore.

The complex interplay between air pressure and surface tension results in different levels of water in two arms of this modified U-tube. This simple experiment clears our misconception that in any U-tube like structure, the water level will always be the same in two arms.

Hope you learned something new today and understood the process of convection currents. For more exciting experiments about math’s and science subscribe to our YouTube channel.


Team: Ashok Rupner, Chaitanya Mungi, Neha Apte, Sajeda Sayyad_Shaikh, Pinki Saha, Students of NCL School Pune, Dr. B N Das