Patterns in a spinning wheel Why do we see patterns on a rotating wheel with spokes which seem to rotate counterclockwise or clockwise as and when the wheel accelerates or deaccelarates. What I mean is the patterns like this
 A: Consider a wheel with just 4 spokes at 90 degrees to eachother, for simplicity.
Your eyes / cameras and such perceive motion through series of 'snapshots' (frames on a film). If you see a spoke in nearly the same place as before, you would assume it is moving and has moved only by "that much".
If the wheel spins in a way that each frame shows the same alignment of the spokes, the spokes appear to stand still. For our example wheel, that's some multiple of 90 degrees per-frame (including 0 and negatives for opposite-direction spins).
If the wheel spins in a way that every second frame does that, the wheel will appear to be spinning at its fastest. The other frames will also show the same picture as eachother but the alignment will be half-way which in this case is 45 + a multiple of 90 degrees.
The important thing to keep track of is how much each spoke appears to move by between each frame. If it's as much as the angle between spokes, they don't seem to move, and if it's half that amount, the movement appears to be a maximum. And the apparent direction will appear to be the slower one of the two.
With that in mind consider this wheel at low speeds clockwise, say 20 deg per frame. Clearly the spokes appear to be moving clockwise (20 vs 90-20=70). But if the speed was 70 deg clockwise, it would appear as 20 deg counter-clockwise (90 - 70). For this reason half-way is indistinguishable: 45 = 90 - 45.
Assuming the wheel is accelerating in CW direction, it will appear as such:


*

*motionless

*slowly moving CW

*rapidly moving CW

*rapidly moving, direction unclear

*rapidly moving, CCW

*slowly moving CCW

*"motionless"

*slowly moving CW


and so on
