Final answer:
Many drops of water can fit on a penny due to surface tension, where water molecules attract each other and form a 'skin' allowing water to pile up. The huge number of water molecules contained in a small drop permits a substantial amount of water to fit on the penny's surface despite its size.
Step-by-step explanation:
The reason why so many drops of water fit on a penny is primarily due to the concept known as surface tension. This phenomenon occurs because water molecules are attracted to each other and tend to stick together, creating a sort of 'skin' at the surface. When water is dropped onto a penny, this surface tension allows the water to pile up into a dome shape without spilling over. The cohesive forces between water molecules are strong enough to hold the water together even when it extends slightly above the penny's surface. To further understand this, consider that a penny, while small in size, consists of a vast number of atoms (approximately 28 sextillion in a copper penny), which demonstrates the concept that you need more of a smaller unit to match a larger unit. In terms of water molecules, a single drop contains an extremely large number of them, allowing for a significant number of drops to fit on the penny's surface. Additionally, in zero gravity, water forms a sphere, which is the shape with the least surface area, but on Earth, gravity distorts this and we see water piling on the penny due to surface tension and gravity.
The phenomenon of water forming a dome or holding a convex shape on a penny is due to surface tension. Surface tension is the cohesive force that causes the molecules at the surface of a liquid to stick together. In the case of water, the molecules are attracted to each other, creating a thin, elastic "skin" on the water's surface.
When you carefully place drops of water onto a clean penny, the surface tension prevents the water from spreading out and allows it to form a dome-like shape. The cohesive forces between water molecules are strong enough to resist the pull of gravity, allowing the water to stay suspended on the penny. This effect is more noticeable when the penny is clean and wettable, as contaminants or oils on the surface can interfere with surface tension.
The number of drops that can fit on a penny depends on the size of the drops and the cleanliness of the surface. It's a simple yet fascinating demonstration of surface tension in action.