Concepts of Physics

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

Why the Tumbler Stick to your Hand?

Objective

To get familiarize with the pressure difference.

Apparatus

a glass tumbler (with small mouth), a piece of paper, a matchbox

Procedure

Take a small piece of paper. Light the paper with a matchstick and place it inside the glass. When the flame is about to extinguish, place your palm tightly on the mouth of the glass. Keep it pressed till you feel some suction on your palm. Now, raise your hand and you will find that the glass stick to your palm.

Discussion

There was air inside the glass before the burning paper was put inside the glass. When the paper was burnt, carbon dioxide was produced and oxygen was consumed. So when you placed your palm over the glass, supply of air was cut and flame was extinguished. By placing the burning piece of paper in the glass, the air inside the glass was heated and expanded. The expansion made the air rush out of the glass. The extinction of the flame caused the air inside the glass to cool down. This reduces the pressure inside the glass and the palm of the hand was sucked in i.e., a partial vacuum was created inside the glass which made the glass to stick to the palm.