anchor.diff:  		angular_momentum = AngularMomentum
   	} = State,
   
  -	NextPosition = Position + Velocity * TimeDelta,
  -	NextVelocity = InitialVelocity + Force * TimeDelta,
  -	NextOrientation = Orientation + Spin * TimeDelta,
  -	NextAngularMomentum = AngularMomentum + Torque * TimeDelta,
  +	{SpinW, SpinX, SpinY, SpinZ} = Spin,
  +	{OrientW, OrientX, OrientY, OrientZ} = Orientation,
  +	NextPosition = vector:add(Position, vector:multiply(TimeDelta, Velocity)),
  +	NextVelocity = vector:add(InitialVelocity, vector:multiply(TimeDelta, Force)),
  +	%XXX: I have no idea if/how this works, but it's what the example code did...
  +	NextOrientation = {
  +		OrientW + SpinW * TimeDelta,
  +		OrientX + SpinX * TimeDelta,
  +		OrientY + SpinY * TimeDelta,
  +		OrientZ + SpinZ * TimeDelta
  +	},
  +	NextAngularMomentum = vector:add(AngularMomentum, vector:multiply(TimeDelta, Torque)),
   
  -	NextState = State#physical{
  +	State1 = State#physical{
   		position = NextPosition,
   		linear_velocity = NextVelocity,
   		orientation = quaternion:unit(NextOrientation),
   		angular_momentum = NextAngularMomentum
   	},
   	%TODO: Should _NextAngularVelocity even be returned?
  -	{NextSpin, _NextAngularVelocity} = update_state(NextState),
  +	{NextSpin, State2} = update_state(State1),
   
  -	{NextForce, NextTorque} = forces(TimeDelta, NextState),
  +	{NextForce, NextTorque} = forces(TimeDelta, State2),
   
  -	{NextVelocity, NextForce, NextSpin, NextTorque, NextState}.
  +	{NextVelocity, NextForce, NextSpin, NextTorque, State2}.
   
   %% ------------------------------------------------------------------------
   
  
positive.code: %FIXME: This should be a callback so the behavior can do stuff like target-velocity calculations.
  forces(_TimeDelta, State) ->
  	#physical{
  		force_abs = ForceAbs,
  		force_rel = ForceRel,
  		orientation = Orientation,
  		torque_absolute = TorqueAbs,
  		torque_relative = TorqueRel
  
negative.code: % -------------------------------------------------------------------------
  
  -include("log.hrl").
  -include("pre_physics.hrl").
  
  %% ------------------------------------------------------------------------
  %% External API
  