Penny Activity for After-School | Extended Notes

How many drops of water can a penny hold? This science activity demonstrates surface tension in action! Have students make their predictions, and then conduct the experiment to see whose hypothesis was correct.

Materials:

• Water
• Eyedropper
• Pennies
• Pencil and paper
• Paper towels (for clean up)

Instructions:

1. Before starting the experiment, have students use the pencil and paper to record their predictions.
2. Place the penny on a flat surface.
3. Use the eyedropper to draw water and carefully place one drop of water on the penny. Record what happened.
4. Keep adding one drop at a time until the water runs over the edge of the penny.
5. Record your data.
6. Test the experiment on three different pennies and figure out the average number of drops that can fit on a penny. Who had the closest prediction? Did anyone guess the exact number of drops?

Lesson:

Surface tension is described as the cohesion between water molecules caused by hydrogen bonding - when hydrogen atoms of one molecule attract the oxygen atoms of another molecule. When you add water drops on the penny, surface tension causes the drops to “stick together” and pile up into a dome. As you add more drops, the force of gravity becomes stronger than the force of attraction among the water molecules at the surface. This causes the water to spill over the edge of the penny.

This activity was adapted from Summer Program Tips, Strategies & Activities for School-Agers 5-14 Years-Old (now sold via Gryphon House).