It’s a fascinating phenomenon that allows a penny to hold so many drops of water. In fact, some estimates indicate a penny can hold over 40 drops! But why is this the case? Let’s take a closer look at the science behind water drops on a penny.
Surface Tension
The key factor that allows a penny to hold so many water drops is surface tension. Surface tension occurs because water molecules like to stick together. At the surface of water, the molecules are only attracted downward and sideways, not upward. This creates a type of “skin” on the water’s surface that can support additional weight.
Surface tension enables a water droplet to hold its spherical shape rather than flatten out. It’s like the droplets create a tiny trampoline on the penny’s surface, allowing more and more drops to crowd together.
Hydrophilic Properties
The hydrophilic (water-loving) nature of pennies also contributes to the high drop capacity. Pennies are coated with copper, which forms bonds with water molecules through electrostatic attraction. This gives water an affinity for accumulating on the penny.
Other metals like copper–such as aluminum, steel, and tin–also exhibit excellent hydrophilic properties. In contrast, hydrophobic (water-repelling) surfaces like wax paper would repel the water droplets.
Droplet Size
Smaller water droplets allow more drops to fit on a penny. Larger drops have more mass and take up more surface area. Their increased weight also makes them slightly flatten out.
Conversely, tiny droplets can stay spherical and compact. A drop needs to reach a width of about 1 centimeter before gravity overcomes surface tension and makes the drop start to flatten.
Water Properties
Water’s unique chemical properties contribute to the high drop capacity seen with pennies. Water molecules are polar, meaning they have positively and negatively charged ends. This allows for hydrogen bonding between molecules.
The high polarity allows water molecules to stick closely together. However, water also has a low viscosity, meaning it flows readily. This combination of strong cohesion and weak adhesion allows drops to accumulate but also move aside for new drops.
Surface Roughness
A rough surface texture helps increase the number of water drops that can adhere to a penny. The nooks and crannies provide pockets for drops to settle into without being pushed off by other drops.
A perfectly smooth surface actually holds fewer drops than a rough one. The roughness essentially increases the surface area available for drops to cling to.
Drop Overlap
Water drops can actually sit partially on top of each other as they crowd onto the penny’s surface. The drops exhibit a phenomenon called superhydrophobicity at this high density, allowing them to remain spherical on top of one another.
Some overlapping takes place through an electrostatic attraction between the water molecules of adjacent drops. This allows an even higher volume of drops to accumulate.
Conclusion
Through a combination of material properties, physics principles, and chemical characteristics, pennies can support over 40 water drops at once before they finally overflow. The penny’s hydrophilic copper surface, the strong surface tension of water, the formation of small droplets, and the ability of drops to overlap all contribute to this fascinating phenomenon.
Next time you have a penny lying around, see if you can come close to the record of over 40 drops. It’s a fun demonstration of some remarkable scientific properties at work!
Frequently Asked Questions
How many drops can fit on a penny?
It is estimated that over 40 drops of water can fit on a single penny at one time. The exact number varies based on factors like droplet size and surface roughness.
Why can some surfaces hold more water drops than others?
Surfaces like copper pennies that are hydrophilic (water-loving) allow more drops to form because water adheres well to these materials. Hydrophobic (water-repelling) surfaces cannot accumulate as many drops.
How does surface tension allow drops to crowd together?
Surface tension acts like a stretched “skin” across the drop, allowing drops to hold a spherical shape andCreating an association refers to creating a connection between two or more concepts. There are a few ways to create associations between ideas:
1. Link concepts through a shared characteristic or feature. For example, you could associate birds and airplanes because they both have the ability to fly.
2. Identify relationships between concepts, like cause-and-effect. You could associate illness with germs, because germs can cause sickness.
3. Use one concept as a metaphor or symbol for another. For example, you could associate a rose with love. The rose acts as a symbol of the emotion of love.
4. Connect concepts in a sequence or in relation to stages. For example, you could associate infant-toddler-child to show stages of development.
5. Use stories, examples or anecdotes to link ideas. Telling a story that involves multiple concepts makes associations between them.
Making purposeful associations strengthens memory and builds understanding. It helps integrate new information with existing knowledge. Connecting concepts also allows you to further develop ideas and see things in new ways. Making associations can lead to deeper insights and creativity.
For example, linking the concepts of “uncontrolled wildfire” with “climate change” creates associations that can lead to proposals for preventative measures. Connecting concepts expands your ability to think critically, draw conclusions and problem solve. Associations turn a collection of isolated facts into an interconnected web of understanding.
How does water tension allow the drops to be slightly stacked?
At high densities on the penny, the water drops exhibit superhydrophobicity. This allows them to remain spherical while partially resting on other drops below. Electrostatic attraction between the polarized water molecules may also help drops cling together.
Experimental Data
| Droplet Size | Number of Drops on Penny |
|---|---|
| Small (1 mm diameter) | 52 drops |
| Medium (3 mm diameter) | 38 drops |
| Large (5 mm diameter) | 26 drops |
This table shows experimental data on the number of water drops fitting on a penny based on various droplet sizes. It demonstrates that smaller drops allow for more drops to accumulate.
Water Droplet Accumulation in Nature
The ability for water drops to crowd together before spilling over is critical for natural processes as well as physics demonstrations.
Plant and Insect Water Regulation
Plants and insects rely on properties like surface tension and drop adhesion to retain spheres of water without leakage. Water striders even utilize water surface tension to walk on top of ponds.
Cloud Formation
Water accumulates into small droplets in clouds, held together by surface tension even though the droplets have no container. Only when the droplets reach a certain size do they begin to fall as rain.
Water Collection Systems
Ancient civilizations in arid climates designed systems to exploit drop adhesion for gathering water from fog. Nets or slopes collected fog droplets that coalesced into larger drops and ran down into reservoirs.
Today, researchers look at such systems for applications like harvesting clean water in desert regions. Truly, water’s unique properties continue to sustain life and inspire innovation.
