2D Physics (RigidBody2D)

jgrauman

Hi all,

I am trying to figure out the physics of RigidBody2D. In particular, it would be nice to know the units for the various physical aspects so I can figure out how they relate to each other. RigidBody2D has mass, force, torque, impulse, linear_velocity, angular_velocity.

From physics we have: force = mass acceleration, impulse = force time, acceleration time = velocity, velocity time = distance, etc.

So here are some specific questions (assume frictionless environment, ie no damping):

Will apply_central_impulse() result in the same velocity as add_central_force() applied for 1 second?

If I apply_central_impulse(1000) to a RigidBody2D with a mass of 100, what will the velocity be?

If a RigidBody2D has a velocity of 100, what central impulse would I need to stop it if its mass is 100?

Thanks for any clarification.

I could try some experiements to figure it all out, but if anyone knows offhand the units of the various physics in Godot, that would be helpful.

jgrauman

Ok, I figured at least some things out. Most of my confusion was over the fact that an impulse in Godot is different than the physics definition. Apparently, an impulse in Godot directly gives a certain velocity, no matter what the mass of the object...

jgrauman

But it seems really weird, apply_torque_impulse() is mass dependent, while apply_central_impulse() is not???

jgrauman

Ok, I figured out pretty much everything. For those interested, I think this is how it all works...

My experiements were getting all wrong results because I wasn't applying and adding forces in func _physics_process(delta):

linear_velocity is measured in pixels per second, angular_velocity is measured in radians per second. Impulses are defined like in standard physics, an impulse is equivalent to applying a force for a second.

Hope that helps anyone coming along, that took a while to figure out!