The reason a coin can float on top of the water in a glass is due to the phenomenon called surface tension of water. Water molecules at the surface are attracted to each other strongly (cohesion), creating a kind of "skin" or elastic layer on the surface. This surface tension is strong enough to support the coin's weight as long as the coin is placed carefully and does not break this layer. Although the coin itself is denser than water and would normally sink, the surface tension effectively holds it up by resisting the coin pushing through the water surface. This effect is delicate, so if the surface tension is broken (e.g., by adding soap or disturbing the water), the coin will sink. In summary, the coin floats because the surface tension of the water holds it up , despite its density being higher than water.
