The propagation of waves on the liquid surface is controlled by 3 external forces: i. Gravity ii. Surface tension and iii. Hydrostatic pressure. If gravity plays the main role, we call the waves gravity waves. These waves (a) are deep waves; (b) have long wavelengths; and (c) are of comparatively small curvature. When the main controlling factor is the surface tension, the waves are called **capillary waves.** If both the gravity and surface tension control the propagation of the waves, we call the waves **ripples.** They have small wave lengths. #### Velocity of Gravity Waves