Calculating Surface Tension with Capillary Waves

Surface tension is the tendency of a fluid to reshape itself to occupy the smallest possible surface area. This is why raindrops are round. For a flat surface of water, any deflection is pulled back even to the surface. If any overshooting occurs, the surface will bob back and forth, creating a wave. Capillary waves are waves having surface tension as the primary restoring force; their wavelengths are in or below the centimeter range. By measuring the properties of such a wave, surface tension can be measured. We developed an apparatus that produced capillary waves to measure the surface tension of water. Unlike some other experimental setups, ours can work on any fluid regardless of polarity. We examined the dispersion relationship of the capillary waves produced by our apparatus to make the measurement, and found the surface tension of water to be 71.5 dynes/cm, which is within 5% of the literature value of 72.8 dynes/cm.