Contact-Angle Race

Drops bead, spread, or soak differently. Ask students to predict what will happen. Put equal drops on different surfaces. Key idea: Balance between cohesion and adhesion depends on surface chemistry. Ask: Why is the same water a different shape on each surface? Safety and cleanup: Small drops; nonbreakable surfaces. https://www.google.com/search?q=%22Contact-Angle+Race%22+science+demonstration+experiment