Imagine a cup of black coffee. Add a spot of cream. Watch. The white glob swirls, tendrils stretch to the rim and get thinner. Black and white meld to milky brown but black patches remain, white tendrils linger. Grab a spoon. Stir. The patches and tendrils disappear. Sip. Enjoy.
The interactions of motion that mix the coffee and cream are difficult to understand, says Dan Rudnick, an oceanographer at the Scripps Institution of Oceanography at the University of California in San Diego. His task is even more difficult. He and his colleagues are on a quest to understand how mixing happens in the oceans.