Materials
- 1 penny or dime
- Water
- Dropper
- Flat surface
Instructions
- Place the penny or dime on a flat, level surface.
- Fill the dropper with water.
- Slowly add one drop at a time to the top of the coin.
- Count each drop carefully as you add it.
- Watch the water form a rounded dome on the coin.
- Continue adding drops until the water spills over the edge.
- Record how many drops fit on the coin before it overflowed.
What’s going on?
- Water molecules attract each other strongly. This attraction is called cohesion. At the surface of the water, cohesion creates surface tension, which acts like a stretchy skin.
- Because of surface tension, water can pile up into a rounded dome on the coin instead of spilling immediately. The dome grows until gravity overcomes surface tension and the water spills over.
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