The formation of a fluid bubble on a penny is an example of cohesion, not adhesion.
When a penny is wetted with a small amount of water, the water molecules are attracted to each other by cohesive forces, which are intermolecular forces that bind molecules of the same substance together. As a result, the water molecules tend to stick to each other rather than to the surface of the penny, forming a rounded shape or a "bubble".
The cohesive forces between water molecules are strong enough to overcome the gravitational force acting on the small volume of water on the penny, which is why the water does not run off the penny. This phenomenon is also known as surface tension, which is the cohesive force that acts between molecules at the surface of a liquid.
In contrast, adhesion refers to the intermolecular forces that bind different substances together, such as the attraction between water molecules and a surface. If the adhesive forces between water and the penny were stronger than the cohesive forces between water molecules, the water would spread out over the surface of the penny, rather than forming a bubble. However, in the case of the penny and water, the cohesive forces between water molecules are stronger than the adhesive forces between water and the penny, resulting in a fluid bubble.