Newton's second law could be stated either as , or as force equals time rate of change of linear momentum. For simple rotational motion the corresponding law is stated as , or torque equals time rate of change of angular momentum. Momentum is conserved when there is no external force. Angular momentum is conserved when there is no external torque. To test this, sit on a rotating stool with your hands in by your sides. While rotating, extend your arms away from your body. Repeat while holding masses in your hands. Describe the effects. Give an explanation.