When you stir a cup of tea, the leaves collect in the centre rather than being flung to the edges, even though spinning should push them outward. The stirring sets the whole liquid rotating, but friction against the cup's bottom slows the fluid nearest the floor. That slower layer is pushed inward by the faster-moving liquid above, creating a circulating flow that sweeps along the bottom toward the middle and then rises. The leaves are carried by this flow and settle at the centre. Physicist James Thomson identified the cause in 1857, and Albert Einstein gave a fuller explanation in 1926 while studying how river banks erode.

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.