The first sonic boom was cracked by a whip

Long before aeroplanes, humankind was already breaking the sound barrier. A whip's crack isn't the leather striking itself: it's a tiny sonic boom.

When the arm sends a wave down the whip, the energy travels toward the tip, which grows ever thinner and lighter. To conserve that energy, the end accelerates more and more, until it passes 1,200 kilometres per hour: faster than sound. The «crack» we hear is the same physics as the roar of a fighter jet crossing the sky.

So the first human-made object to break the speed of sound wasn't an aeroplane in 1947. It was, most likely, a length of braided leather thousands of years ago.

Source: Physical Review Letters