Asked by: Alan Blackwood, by email
Anyone who’s seen a film like Butch Cassidy and the Sundance Kid, which features a character running along a train roof, will know it’s possible – as long as the train isn’t moving too fast. As speed picks up, the air blowing over the carriages becomes stronger, along with their rattle and roll, and running becomes all but impossible.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.
