Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Gravity Defying Test Tube

Objective

To create low pressure area inside the test tube.

Apparatus

two test tube of slightly different dimeters so that one can slide inside the other (like a piston).

Procedure

Fill the larger test tube three-fourth with water. Push the smaller test tube half way in it. Keep holding the outer test tube and invert the setup. As water starts coming out through the gap between the two test tubes, the smaller test tube rises.

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Discussion

Water falls down through a very narrow gap between the test tubes leaving no space for air to enter. This creates a low pressure region inside the larger tube. The atmospheric air, which is at higher pressure, forces the inner test tube to move up.