Why do wheels sometimes seem to move slowly in old films?

Rollin' rollin' rollin'... wagon wheels in old movies sometimes appear to move in slow motion. 

29th April 2017
Why do wheels sometimes seem to move slowly in old films? (Getty)

Asked by: Robin Chambers, Preston

Films are shot as a series of individual frames taken at around 24 per second. If the wagon wheel is rotating at precisely the right rate, then a spoke in one frame will have been taken up by another spoke in the next frame, creating the impression the wheel is stationary. If they’re slightly out of sync, however, the wheels will appear to move in slow motion. 

 


SFQASubscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun facts.