Final answer:
Water has a higher surface tension than rubbing alcohol, allowing more water drops to fit on a penny. Rubbing alcohol has a lower surface tension, causing its drops to spread out and take up more space on the penny.
Step-by-step explanation:
When considering why more water drops could fit on a penny compared to rubbing alcohol, it's important to understand the concept of surface tension. Surface tension is the force that holds the molecules of a liquid together at its surface. Water has a higher surface tension than rubbing alcohol, which means that the water molecules are more strongly attracted to each other at the surface, forming a more cohesive drop.
Because water has a higher surface tension, it can form smaller and more compact drops compared to rubbing alcohol. When drops of water are placed on a penny, their surface tension allows them to maintain their shape and sit closely together, enabling more drops to fit on the penny.
On the other hand, rubbing alcohol has a lower surface tension, so the drops spread out more and are less cohesive. This causes rubbing alcohol drops to be larger and take up more space on the penny, resulting in fewer drops being able to fit on it.