Have some fun with your photography.

• Set your SLR to S/Tv mode
• Select a shutter speed of 1/10th second.
• Use minus one stop exposure compensation
• Use a zoom lens
• Use flash
• Now get ready. Prefocus on your subject with your lens mid-range (eg on an 18-55mm lens, set to 35mm).
• Zoom to telephoto, and then rapidly zoom out all the way. In the middle of this zooming action, click.

This is trial and error, but you will succeed in the end, with shots like this one, fo a student who recently kindly volunteered:

The flash “freezes” the subject, but your background shows the zooming effect.