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Wheels going backwards on TV illusion

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R1Geezer | 11:40 Fri 08th Oct 2010 | Science
7 Answers
Now it's common knowledge what causes this but I noticed something the other day whilst watching a car program. The wheels in question were going backwards as usual but there was the circle of wheel nuts near the centre actually going forwards at the same time. Now I know that the inner part would be going slower than the outer but given that TV is a series of still pictures how can it effectively show the outer wheel not connected to the innner, ie by them both rurning in different directions. ie each individual picture must have both bits of the wheel on it! Anyone explain this? thanks


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Because the inner part of the wheel doesn't have to travel as far as the tyres and so will display differently on each frame. Depending on the speed of the car/film, it will appear as though parts of it are moving differently.
Question Author
yes SB but what I'm saying is that on each individual frame they would be attached to each other. Is this a film effect or some sort of optical illusion?
I saw Hummer at Anfield which had an inner rim that rotated opposite to the wheels.
Could that account for it?
I've seen wheels with six spokes and five nuts. At certain rates of rotation, these can appear to rotate in opposite directions under strobe lighting. For example . . .
In the next frame the second spoke has taken a position slightly ahead of where the first was while the second nut would appear to be lagging behind where the first was.

To visualise what's taking place, draw a picture with five nuts 72 (360/5) degrees apart and six spokes 60 (360/6) degrees apart, turn the image 65 degrees then compare the placements of the nuts and spokes . . .
Question Author
Thanks Mibn, it was a ferrari 599:
it does have 5 nuts and 6 groups of spokes so that is a feasable explanation. thanks
Question Author
yep that's the one

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