Dot Physics

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.


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.


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.


Looks fairly constanty. Here is my next throw.


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


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


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.


  1. #1 Chris
    January 20, 2010

    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.

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