Egypt

In an Egyptian tomb, a painting nearly 4,000 years old shows a man pouring water onto sand.

He’s standing at the front of a sledge. Behind him, a giant statue is being hauled along by rows of men.

Physicists in Amsterdam wanted to understand why. They pulled heavy sledges over dry and damp sand. On dry sand, a ridge built up in front of the sledge and held it back. With just the right amount of water, the grains stuck together, the sand grew firmer, and the pulling force needed was cut in half.

The man with the water jar may have made the work half as heavy for everyone pulling.