23 August 2015

The rockfall physics of Wile E. Coyote and the Road Runner

Posted by Dave Petley

Road Runner

Road Runner

The Physics of Road Runner

The classic Warmer Brothers cartoon featuring Wile E. Coyote and the Road Runner involved the repeated attempts by the hapless Coyote to capture a Road Runner bird, involving a range of increasingly outlandish contraptions, that without fail, backfired spectacularly.  Wile E. Coyote frequently attempted to use rockfalls in various guises as a device to ensnare the Road Runner.  I came across two notable examples on YouTube:

1. The Rolling Boulder

Pushing a rolling boulder down a slope to catch the fast-moving Road Runner is a challenge of timing:


Wile E. Coyote clearly underestimated the long runout effect of some large landslides, such as rock avalanches.  Mind you, the friction coefficient of this boulder would be a challenge for even the most seasoned landslide specialist.

2. The rockfall

In this case Wile E. Coyote tries to catch the Road Runner with a classic rock topple, with a nicely placed keystone:


Even though Wile E. Coyote has modeled the system, he demonstrated here that predicting the likely behaviour of any rockfall is difficult, especially when the blocks are irregular in shape!

I am very glad I don’t have to try to understand and forecast landslide behaviour in cartoon land!