Motion of a Dart in Bloons

I stumbled on this flash game Bloons. The basic idea is that you (the monkey) throw these darts and try to pop some balloons.

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Well, what is the motion of these darts like? Is it constant acceleration? Time to pull out the free and awesome Tracker Video Analysis.

I threw a few shots and captured the screen with Mac OS X's quicktime X (which does screen recordings now). Then I chose a few of the motions to analyze. I was going to use Tracker's autotracker feature, but I am not sure how well it would work since the dart changes orientation (of course I didn't even try this to see if it would work - I don't know why). One other important thing. I scaled the video with the monkey (height) being 1 unit. Here is the first shot - thrown mostly vertical.

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The data looks a little rough. I am not sure why. It could be the game, or it could be my screen recording. Maybe it was just too much for my computer. Anyway, this gives a vertical acceleration of -4 monkeys/s2. What about the horizontal acceleration? Here is the horizontal vs. time plot.

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Looks fairly constanty. Here is my next throw.

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Same dart, different throw, different vertical acceleration. This time the acceleration is around -9 monkeys/s2. What about the horizontal acceleration?

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Again, seems ok. Last throw. This one is at a very low angle. Here is the vertical position-time plot.

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Again, a different acceleration. I wonder if the acceleration of the dart is related to the angle of the throw, the initial velocity, or both.

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It seems like a systematic error when looking at the horizontal plots - they have the same features. My guess would be the problem lies somewhere in the analysis since I think your eye would have detected that point in the middle where the dart seems to stop and a go backwards for a split-second.