Determine angular momentum from angular velocity for SKSpriteNode

Question

I have an node in space (no angular dampening, no friction, no gravity) and I apply a torque to it (20 newton meters) over 1 second. It begins to spin and will continue forever. If I apply an inverse force (-20 newton meters) it comes to a complete stop.

If I don't know how much angular torque was applied initially (for instance it collided with another object), how can I determine what the inverse torque to apply would be in order to bring the object to a stop? I tried angularVelocity*mass, and this is close... but always a little shy (like I'm missing something):

-physicsBody!.angularVelocity*physicsBody!.mass

How can I determine Angular Momentum (torque) to use to remove all object rotation?

Answer 1

In my games I use active braking to manage stopping a node's motion over time. I do this in the update() function. For your requirements, I present this answer:

let X = -0.2  // This needs to be customized by your needs .. how fast you want to stop.
var need_braking_list : [SKSpriteNode] = []   // Append your spinning nodes here

override func update() {
    for (index,node) in need_braking_list {
        // We're almost stopped, so force a stop or this goes on forever.
        if node.physicsBody?.angularVelocity < 0.1 &&
               node.physicsBody?.angularVelocity > (-0.1)
        {
             node.physicsBody?.angularVelocity = 0
             need_braking_list.removeAtIndex(index)
        // Apply some braking ... screeech
        } else {
            let impulse_factor = node.physicsBody?.angularVelocity * (X)
            node.physicsBody?.applyAngularImpulse(impulse_factor)
        }
    } 
}

Hope this helps!