MythBusters Episode 12: Break Step Bridge, Toothbrush Surprise, Rowing Water Skier

Soldiers marching in unison can cause harmonic oscillation in a bridge and cause it to collapse.

plausible*

Adam built a 60-foot (18 m) by 6-foot (1.8 m) suspension bridge from metal tubing and nylon rope, while Jamie built 12 dummy soldiers out of air-powered actuators and combat boots. In the initial test, the soldiers moved far too slowly due to a disconnected hose. During the second and third tests, the soldiers stomped too hard on the bridge, causing the bridge to collapse from impact without any harmonic vibration.

* The original result was “busted” but when revisited in Myths Revisited it was changed to “plausible.”

A rowing eight can pull a water skier at sufficient speed for him/her to stay upright.

confirmed

Adam and Jamie recruited Stanford University’s rowing team to help test this myth. After several tries Jamie was able to stay upright for over 40 seconds, with only a few hours experience in water skiing.

Fecal coliform bacteria can grow in toothbrush bristles.

confirmed

Fecal coliform were indeed found on all the test brushes, including the control ones. However, none were of a level high enough to be dangerous, and experts confirm that such bacteria are impossible to completely avoid.