When a drinking glass slides across a wet surface like a countertop or table by itself, it's due to a phenomenon called the "water adhesion effect" or "capillary action." This effect occurs because of the intermolecular forces between water molecules and the surface of the countertop or table.
Here's a simplified explanation of how it works:
Wet Surface: When the surface of the countertop or table is wet, a thin layer of water forms on it.
Adhesion: Water molecules have adhesive forces or attraction to the surface molecules of the countertop or table. This adhesion is stronger than the cohesive forces between water molecules.
Capillary Action: As the drinking glass moves across the wet surface, it pushes the water ahead of it. Due to adhesion, the water molecules stick to the surface and create a thin film of water between the glass and the countertop.
Surface Tension: Water molecules have cohesive forces between each other, resulting in surface tension. The surface tension of water helps hold the water film together and allows it to act as a lubricant.
Reduced Friction: The water film between the glass and the countertop reduces the friction between them, making it easier for the glass to slide across the surface by itself. The thin layer of water acts as a lubricating layer, allowing the glass to glide smoothly.
It's important to note that this effect occurs when the surface is sufficiently wet, and the glass has a smooth bottom that allows the water film to form. If the surface is only slightly damp or the glass has a rough or non-smooth bottom, the effect may not be noticeable or may not occur at all.
This phenomenon is not limited to drinking glasses and can occur with other objects as well, depending on the surface and conditions.