# Accelerometer and/or Gyroscope for gesture sensing

I want to sense 3D motion (gesture). I have 3 axis accelerometer. But I am confused if I need a gyroscope or not for orientation and rotation sensing.

1. Isn't it possible to measure them from accelerometer alone? Because when the sensor rotates along one axis (say z-axis), there will be change in y-axis and x-axis output in accelerometer.

2. Is gyroscope really necessary or is it just easier if I have one?

Consider an accelerometer experiencing a net acceleration of gx - gz.
4. The sensor is rotating about some point, moving with a non-constant velocity such that the acceleration is gx - gz.