![Gyroscope](https://i0.wp.com/www.exploringarduino.com/wp-content/uploads/2013/06/dual-axis-gyroscope.jpg?resize=400%2C337&ssl=1)
Image courtesy of RobotShop
Use a gyroscope to detect rotational acceleration. A 3D analog gyroscope returns three analog voltages, each corresponding to angular acceleration around a particular axis.
Buy a Triple-Axis analog gyroscope from RobotShop.