Back-of-the-envelope Physics Today

Leo shrugged, finally feeling the adrenaline fade. "The math is simple. It's the envelope that's hard to find."

The foreman looked at Leo, then at the utility bill. "You did this with a pen and a light bill?" Back-of-the-Envelope Physics

Leo didn't finish his espresso. He bolted out the door, waving the envelope like a white flag. He reached the foreman just as a loud crack echoed through the street. Leo shrugged, finally feeling the adrenaline fade

: He squinted at the cable. It looked like 2-centimeter thick steel wire rope. From memory, the breaking strength of a 2cm steel cable was somewhere around Back-of-the-Envelope Physics

Ten minutes later, the girder was safely back on the ground. A single bolt had sheared halfway through.