Pure Rotation or Rotation about a Fixed Axis
![Lecture content](../sound.png)
Rotation about a fixed axis is also called pure rotation. This results in all points on the body moving in a circular paths around the central fixed axis. All points on the body, except the points along the fixed axis, may experience linear and angular acceleration.
![](rbnewt_ro_fig1.png)
![Lecture content](../sound.png)
Newton's second law for pure rotation
∑F = maG
Now that each point on the body may experience a different acceleration, unlike the case for pure translation, we must take care to use the acceleration of the body's mass center (G) in Newton's second law. We can use the following kinematic relationship to determine the acceleration of G.
aG = α x rG/O - ω2rG/O
![Lecture content](../sound.png)
Moment equation for pure rotation
∑MO = IOα
Note that the moments and mass moment of inertia are with respect to the fixed-axis through O.