This filter, available through Filters/Blur/Motion Blur, makes the contents of an image look as if they were in motion.
In the Parameters box of the "Motion Blur" dialog you can do the following:
Set the extent of the blur (between 0 and 255) by sliding the Length slider.
Use the Angle slider to set the direction of the blur.
In the Blur Type box choose from these options:
Linear blurs in straight lines. (Note that when you use Linear, the blur will run in the direction you set and in the opposite direction.)
Radial blurs out from the center of the image.
Zoom blurs within the original area, concentrating the colors according to the setting in Length.
All the changes you make can be seen in the Preview box.
See: