code: function(body, r, n)
  {
      var rcn = vcross(r, n);
      return body.m_inv + body.i_inv*rcn*rcn;
  }
docs: /*
  var apply_bias_impulses = function(a, b, r1, r2, j)
  {
  apply_bias_impulse(a, vneg(j), r1);
  apply_bias_impulse(b, j, r2);
  };