[Dan Holton]

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?

[RD]

It's usually a stroboscopic effect called the http://en.wikipedia.org/wiki/Wagon-wheel_effect#Wagon-wheel_effect_under_continuous_illumination [Links inactive - To make links active and clickable, login or click here to register],
 (nothing to do with http://en.wikipedia.org/wiki/Wagon_Wheels [Links inactive - To make links active and clickable, login or click here to register]  [] )

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 [Links inactive - To make links active and clickable, login or click here to register]

[techmind]

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

[thedoc]

Listen to the answer to this question on our podcast.

[JERRYUUCC]

I ALWAYS SEE THE BACKWARDS SPINNING WHEEL EFFECT OUT IN THE NORMAL DAYLIGHT . . . WHERES THE STROBE-EFFECT IN THAT ?

[David Cooper]

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.

[Annie]

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.

[larrylee]

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 newbielink:http://wheels.net/ [nonactive] 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.