A glass can be filled slightly above the rim with water. Explain why the water does not overflow.
Look up surface tension.
The reason water does not overflow when filled slightly above the rim of a glass is because of a concept called surface tension.
Surface tension is a property of liquids, including water, that causes the molecules at the surface of the liquid to stick together more strongly than those in the bulk of the liquid. The cohesive forces between water molecules create a thin, invisible "skin" on the surface of the water.
When you pour water into a glass, the surface tension pulls the water molecules inward towards the center of the glass. This inward pull creates a concave meniscus, meaning that the water surface curves downward slightly in the middle.
As you continue to pour water, the surface tension counteracts the force of gravity. It allows the water level to rise slightly above the rim without overflowing. The surface tension acts as a sort of "seal," holding the water in place and preventing it from spilling over.
However, it's important to note that this effect is not unlimited. If you pour too much water or disturb the surface, the surface tension will be unable to counteract the force of gravity, and the water will begin to overflow.
So, the reason water does not overflow when filled slightly above the rim is due to the cohesive forces of surface tension, which create a concave meniscus that holds the water in place.