Ok, this is kind of a noob question
I have constructed a small room-like environment (floor and 4 walls), all made from box entities with no mass... so I drop a sphere in the middle of the room and I apply a random linear velocity to it, everything works fine, the sphere bounces a bit, slides and eventually stops, then I want to apply another random linear velocity (as if I was shaking the environment a little bit), but nothing happens, the sphere stays still... am I doing something wrong? am I supposed to use another method other than applyLinearVelocity?
What you're seeing is probably the rest system in action. Once an entity settles down, it will 'turn off.' The applyLinearImpulse method doesn't reactivate an entity. You can set an entity's isActive property to true to force it awake.
Usually, the simplest thing to do is just use the linearVelocity property instead. It will handle the activation automatically. So instead of e.applyLinearImpulse(velocityYouWant * mass), you can just write e.linearVelocity += velocityYouWant.