Why Box2D body doesn't collide? <p>I does some tests with Box2D and stuck with it. Here is my body-construct code:</p> <blockquote> <pre><code> var bodyDef:b2BodyDef = new b2BodyDef(); bodyDef.type = b2Body.b2_dynamicBody; bodyDef.fixedRotation = true; var center:Number = Consts.stageToB2(Consts.worldSize / 2); bodyDef.position.Set(center, center); </code></pre> </blockquote> <pre><code> var body:b2Body = physicWorld.CreateBody(bodyDef); var shape:b2CircleShape = new b2CircleShape(Consts.stageToB2(w) * 0.5); // our monster is in circle shape. var fixtureDef:b2FixtureDef = new b2FixtureDef(); fixtureDef.shape = shape; body.CreateFixture(fixtureDef); </code></pre> <p>I created such two bodies, but they doesn't collide! the debugDraw also doesn't light up the bodies. but when I add an angular velocitiy for one of them:</p> <blockquote> <p>body.SetAngularVelocity(Math.PI / 89);</p> </blockquote> <p>They'll start collide. Could you explain What happens here?</p>