Naked Science Forum

General Science => General Science => Topic started by: Dan Holton on 28/10/2009 17:30:05

Title: Why do car wheels seem to go backwards when illuminated by street lights?
Post by: Dan Holton on 28/10/2009 17:30:05: Dan Holton asked the Naked Scientists:

Hello

Why do car wheels sometimes appear to move backwards when illuminated by street lights, even though the car is going forward?

Dan Holton in Bristol, UK

What do you think?
Title: Re: Why do car wheels seem to go backwards when illuminated by street lights?
Post by: RD on 28/10/2009 17:38:30: It's usually a stroboscopic effect called the wagonwheel effect (http://en.wikipedia.org/wiki/Wagon-wheel_effect#Wagon-wheel_effect_under_continuous_illumination),
(nothing to do with the oversize biscuits (http://en.wikipedia.org/wiki/Wagon_Wheels) [:)] )

However if it was a boy-racer, pimp-my-ride, type car it could actually be spinning hubcaps ... http://en.wikipedia.org/wiki/Spinner_%28wheel%29
Title: Why do car wheels seem to go backwards when illuminated by street lights?
Post by: techmind on 31/10/2009 15:21:09: The streetlights are not emitting light continuously, but normally pulsed in 100Hz flashes (50Hz electricity countries) or 120Hz (60Hz countries).

Then see this thread of a few months ago:
http://www.thenakedscientists.com/forum/index.php?topic=20619
Title: Why do car wheels seem to go backwards when illuminated by street lights?
Post by: thedoc on 04/11/2009 11:50:44: Listen to the answer to this question on our podcast. (http://www.thenakedscientists.com/HTML/podcasts/show/2009.11.01/)
Title: None
Post by: JERRYUUCC on 10/09/2012 02:05:59: I ALWAYS SEE THE BACKWARDS SPINNING WHEEL EFFECT OUT IN THE NORMAL DAYLIGHT . . . WHERES THE STROBE-EFFECT IN THAT ?
Title: Re: Why do car wheels seem to go backwards when illuminated by street lights?
Post by: David Cooper on 29/10/2013 20:34:44: Quote from: JERRYUUCC on 10/09/2012 02:05:59
I ALWAYS SEE THE BACKWARDS SPINNING WHEEL EFFECT OUT IN THE NORMAL DAYLIGHT . . . WHERES THE STROBE-EFFECT IN THAT ?

That would have to be in your eye or brain, reflecting the data transmission rate. You ought to study it and see if you can work out what the frequency is by identifying the speeds at which wheels of moving cars appear to be stationary.
Title: None
Post by: Annie on 30/01/2015 23:57:07: I see this stroboscopic effect in my real life (not just film) all the time - and see or notice it more during daylight hours.i once asked an engineer friend what this phenom was and he told me there was no such thing.
Title: great post
Post by: larrylee on 09/03/2015 13:34:49: While driving, rubber comes off from tires like dust and settles down in the cracks of road. That rubber is in micro particle’s shape that’s why unwatchable. Those particles are washed out during rain or get break down via organic process.
Rate of this process depends on two factors, quality of tire and how roughly you drive your car. Many dealers like wheels.net (http://wheels.net/) and others sell high quality tires that run constantly for long time, but it also depends on the surface of driving. In a plane surface tires give great service but on uneven road chances of being worn out are higher.