posted by dennisn on October 25th, 2008 at 1:16PM
Well, not every backwards movement in the x axis is a backward motion. If you draw a vertical line going through the ball, notice where it meets the *side* wall. It means that every forward movement along the x-axis means a ball moving in a direction FORWARD from that line. In other words, it means that the ball was going *at least* BEHIND that line.
Since there was an actual backwards movement along the x-axis, if you insist that it was going forwards, it would HAVE to have been going towards the side wall, behind that line. (The ball was clearly going towards the front though, further disproving your theory.)
If you draw a horizontal line through the ball, and where it hits the side wall, draw a vertical line, that will give you the maximum allowable backwards movement along the x-axis, which still indicates a forward moving ball. (One that is moving directly to the side wall.) Any larger backwards x-movement would indicate a backwards movement. It's a little hard to do that in these images though, since the ball is very close to the edges.
Furthermore, the vector alone between the ball in frame 90 and frame 91 clearly indicates one of two possible scenarios: (i) the ball has been hit at a sharp 90° angle towards the side wall, or (ii) it is a normal bounce, following it's normal backward movement. And since (i) simply did not happen if you look at the subsequent frames, (ii) must be the case.
Moreover, in frame 90, the bottom tip of your racket, which still hasn't reached the ball, which still hasn't hit the floor, is almost at the same level as the ball. In other words, the ball is still going lower (it hits the floor between frames 90 and 91), while your racket has probably already reached it's lowest point. Although, there aren't enough frames to prove this conclusively, it's just another corroboration of the double-bounce theory.
So conclusive and highly-probable evidence and observational advantage (my angle of view was better) ALL point to a double bounce!
Since there was an actual backwards movement along the x-axis, if you insist that it was going forwards, it would HAVE to have been going towards the side wall, behind that line. (The ball was clearly going towards the front though, further disproving your theory.)
If you draw a horizontal line through the ball, and where it hits the side wall, draw a vertical line, that will give you the maximum allowable backwards movement along the x-axis, which still indicates a forward moving ball. (One that is moving directly to the side wall.) Any larger backwards x-movement would indicate a backwards movement. It's a little hard to do that in these images though, since the ball is very close to the edges.
Furthermore, the vector alone between the ball in frame 90 and frame 91 clearly indicates one of two possible scenarios: (i) the ball has been hit at a sharp 90° angle towards the side wall, or (ii) it is a normal bounce, following it's normal backward movement. And since (i) simply did not happen if you look at the subsequent frames, (ii) must be the case.
Moreover, in frame 90, the bottom tip of your racket, which still hasn't reached the ball, which still hasn't hit the floor, is almost at the same level as the ball. In other words, the ball is still going lower (it hits the floor between frames 90 and 91), while your racket has probably already reached it's lowest point. Although, there aren't enough frames to prove this conclusively, it's just another corroboration of the double-bounce theory.
So conclusive and highly-probable evidence and observational advantage (my angle of view was better) ALL point to a double bounce!
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cameras
posted by pasofol on October 25th, 2008 at 1:36PM I suggest at least 4 different cameras next time.
And decent quality at that; to make any evidence solid.
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