Chapter 21, Problem 48A

An old remedy for a pair of nested drinking glasses that stick together is to run water at different temperatures into the inner glass and over the surface of the outer glass. Which water should be hot, and which cold?

To determine

Whether hot water should be poured into the inner glass or over the surface of the outer glass to detach a pair of nested drinking glasses.

Answer to Problem 48A

Cool water should be poured inside and hot water over the outer one.

Explanation of Solution

Introduction:

Thermal expansion is the phenomenon of change in size/shape of an object in response to change in its temperature. Each material has different coefficients of thermal expansion.

When cool water passes over a surface, it contracts and the hotter one expands. Thus, if cool water is poured inside the inner glass then it will try to contract the glass surface and help in losing its grip on the outer glass. While, at the same time if hotter one is passed in the outer glass or over the surface of it, then it will try to expand both the surface in contact. That is, it will free its grip over the inner glass and expand the outer one. This will help in detaching the nested pair of drinking glasses.

Conclusion: Thus, to lose their grip, cold water should be in the inner glass and hot one in the outer one.