When a droplet strikes a water surface, it displaces water downward and launches a circular ripple that propagates outward as a combination of two wave regimes: tiny, high-curvature ripples (millimeters to centimeters) are dominated by surface tension and are called capillary waves, while larger ripples are dominated by gravity and are called gravity waves. As the ring expands, its energy spreads over an ever-larger circumference, so the wave amplitude decays with distance even before viscous damping removes energy as heat. Where two or more ripple rings from separate droplets overlap, their height displacements add algebraically — crests reinforce crests (constructive interference) and crests cancel troughs (destructive interference) — producing the crisscrossing interference patterns you see when raindrops strike a puddle.

• Capillary (surface-tension) waves dominate at wavelengths below about 1.7 cm on water.
• Gravity waves dominate at longer wavelengths, where restoring force is gravity rather than surface tension.
• Deep-water gravity wave speed scales as v ≈ √(gλ/2π); longer ripples travel faster.
• Water's surface tension is about 0.072 N/m at 20°C, which resists curvature in small ripples.
• Ripple amplitude roughly scales with droplet impact momentum (mass × fall velocity).
• A raindrop typically falls at 2-9 m/s depending on its size before striking a puddle.
• Ripple energy decays with distance (geometric spreading) and over time (viscous damping).
• Overlapping ripple rings from multiple raindrops create the classic crisscross interference seen on puddles.