Use the Motion Blur tool to simulate the blur created by fast-moving objects. Motion Blur is used with both the normal and physical cameras.You can apply motion blur globally (to the entire scene) and then exclude objects in the scene from its effect.
To use motion blur, enable the Motion Blur button in the Action Setup menu and specify motion blur settings.
You can animate the Motion blur button, as well as the Phase, Shutter, and Samples fields. They can be found in the Channel Editor under the motion_blur folder.
See Accumulation Settings in Rendering Tab.