KnowHow Team explains: If a glass slide is placed on another, a layer of air is trapped between their surfaces. The pressure exerted by the air trapped between the two surfaces is almost the same as the atmospheric pressure.This pressure acts on each surface in the outward direction.

The slides are also surrounded by air whose pressure is equal to the pressure being exerted by the air. However, this pressure acts in the inward direction. Since the outward pressure is equal to the inward pressure, they balance each other. As a result, we are able to separate the slides easily.

But if a wet slide is placed on another wet slide, the layer of air is absent. The pressure exerted by the water trapped between the two surfaces is much less than the atmospheric pressure of the air surrounding the slides.

So, in this case, the inward pressure on each surface forces the slides to remain stuck. However, the slides can be pulled apart. The moment we apply sufficient external force, air moves into the space between the two surfaces, balancing the inward pressure.

The question was sent by Soudmick Mukherjee, Burdwan.