Water on a Coin

Using an eyedropper, drops of water are placed on a coin and it's observed how many drops can pile up before spilling over. The activity demonstrates cohesion, adhesion, and surface tension in water compared with other liquids like oil and syrup.

1. Place a clean coin on a flat surface.
2. Use an eyedropper to carefully place drops of water on the coin, one at a time, while counting.
3. Continue until the droplet spills over, then record the number of drops.
4. Wipe off the coin or use a new one.
5. Repeat the process using oil or corn syrup instead of water, comparing the number of drops each liquid can hold.

Drops of water on penny - Kids Fun Science:

📄 Science World - Drops on a Coin: https://www.scienceworld.ca/resource/drops-penny/

• Add a drop of soap to the water to see how reduced surface tension changes the number of drops.
• Try using coins of different sizes (pennies, nickels, dimes) to compare results.
• Perform the same experiment by adding coins one by one into a full glass of water to see how surface tension allows the water to rise above the rim.

• Clean up spills promptly to avoid sticky surfaces from syrup or oil.
• Use only clean coins and avoid putting them in your mouth.
• Dispose of used liquids properly—do not drink them.

• How many drops of water fit on the coin compared to your prediction?
• Why can more drops of water fit on a coin than drops of oil or syrup? (Because water’s cohesive hydrogen bonds create stronger surface tension than nonpolar liquids.)
• What causes the “skin” on the surface of the water droplet? (Surface tension from cohesive forces between water molecules.)
• Would a larger coin hold more drops of water? Why or why not? (Yes, because of a larger surface area, but size is more important than coin value.)
• What effect does soap have on the number of drops that fit? (Soap disrupts hydrogen bonds, lowering surface tension, so fewer drops fit.)