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I have an Android application using JBox2D for physics simulation. The only dynamic object is a 0.07m radius circle, as well as several static circles and rectangles in a total game area of about 20m by 20m. I'm also using a few custom forces through the ApplyForce method.

Whenever any bodies collide, they do collide correctly however they don't bounce; everything just thuds together. All bodies have their densities, frictions and restitutions set (some objects have a restitution greater than 1).

Does anyone have any ideas why these collisions aren't working? I think it might be because the bodies aren't moving fast enough for JBox2D to count as proper collisions (there is a cutoff in Box2D).


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This might be of help Ball to Ball Collision - Detection and Handling stackoverflow.com/questions/345838/… –  Mob Sep 24 '11 at 21:28
what version of the engine are you using? I would recommend trying again with the release, this may have been fixed –  Daniel Murphy Feb 12 '12 at 23:07
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2 Answers

setting Settings.velocityThreshold = 0.0001f; (or very small) solved it for me.

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Is it possible to change this without recompiling JBox2D? I'm using v2.2.1.1 and it's a static final. –  afaulconbridge Nov 25 '13 at 17:24
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I found a partial solution to this - Box2D (at least JBox2D) ignores restitution if the velocity is below a certain threshold - by scaling all my objects up by a factor of 10, the threshold becomes relatively lower, and objects bounce.

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