On Jul 14, 12:22*am, Smitty Two wrote:
In article
,
*harry k wrote:

Nope. *It is strobing. *In some of the old films you can see a wheel
go backwards, slow, forwards. *That is caused by the wheel speed
changing.

Harry K

Have you actually seen the commercials, Harry? I'd be surprised if you
saw them and stuck by your wagon wheel effect hypothesis. In the
screwdriver commercial, it doesn't matter whether you look at the chuck,
the driver bit, or the screw, it's rotating the wrong way, quite clearly
and a very stable rate.

Between camera scan rate, 60 Hz strobing (they use lights outside in
bright sunlight)...as you go through a speed range...the rotating
object may "appear" to go forward and then backwards (even frame by
frame).
bob_v