image

Water drop impact. High-speed photograph of secondary drop formation following the impact of a water droplet on water. The impact causes the surface of the pool to collapse, creating a rush of water inwards and upwards to form a column. Surface tension effects along the column cause a secondary drop to form. Shock waves radiate outwards as concentric circular ripples. (KEYSTONE/SCIENCE PHOTO LIBRARY/FRANK FOX/SCIENCE PHOTO LIBRARY)