why, when u watch a movie, seeing a car drive forward, do the wheels move in the opposite direction?

Answer 1

It's called 'Aliasing' in engineering terminology.
You would understand this phenomenon by comparing speed of the wheels and frame rate of the movie.
Typically, the movie displays 25 frames/second (outside USA, where it is 30 frames/second). This is fast enough for eye not to notice any 'jerks' in the movement.
Now think what happens if the wheel speed is exactly 25 revolutions/second.(rps) You will see the wheel stationery, because in each frame, any given point on the wheel is in exactly same position.
Now if the wheel speed is more, say, 35 rps. Then any given point on the wheel will be slightly BACKWARDS in reference to previous frame. This gives rise to our vision that the wheels are rotating backwards.
But if the speed is 50, i.e., a multiple of framerate, the wheels will again look stationary.
Incidentally, the correct speed of the wheels will only be noticed when the speed is below half of the frame rate. That means 15rps in USA and 12.5rps elsewhere. This is called Nyquist Rate.
You can get more information about this phenomenon (in pictures, to aid comprehension) by searching for 'Nyquist Rate' and 'Aliasing' in Google.

Answer 2

The wheels are actually moving forward. However, they speed in which the wheels are moving is faster than our brain can register, and so it looks like the wheels are moving in reverse. Our eyes focus on a spot on the wheel, but by the time the information reaches our brain and is processed, that point has already moved, and as a result it looks like the wheel is moving backwards. It's a pretty neat phenomenon.

Answer 3

I was going to answer this but ravish has already in much more detail than I could have. He is perfectly correct. You can see the effect even better in old westerns where you watch the spokes of the wagon wheels

Answer 4

Youre question is kinda confusing

Answer 5

"u" ???????????