Using a fast shutter speed or high ISO setting to stop action or taking advantage of the peak point of an event to imply motion are two very good techniques, but what if you're photographing a skateboarder? There's no peak in the action, and think of what a person on a skateboard would look like if photographed at 1/1000 of a second. They'd appear to be balancing on a skateboard with no indication of motion, and possibly suspended in midair.
To give the impression of motion and speed when fast action is moving perpendicular to the camera lens, try panning. With this technique, the photographer uses a slow shutter speed and follows the subject as it passes in front of the lens. The idea is to move the camera at exactly the same rate as the subject. If done correctly, you should get a sharp, or at least partially sharp, subject against a fuzzy background.
In order to pan, the photographer should know the spot where the subject will pass. Ideally, the camera will have the focus-tracking or servo option, found on some single-lens reflex (SLR) cameras. With this setting, the camera continually focuses on the subject until the picture is taken. Not only that, but the camera anticipates the subject's next move, so even during that brief instant that the picture is taken, focusing is still taking place.
When panning with an automatic, manual-focus or digital camera, prefocus on the spot where you anticipate taking the picture. Lock-in on that point with the focus-locking device, or by pressing part way down on the shutter release and holding it there until you're ready to shoot.
In preparation for the shot, the photographer should point his or her feet in the direction of the action point, then pivot at the waist in the direction the subject will be coming from. As the subject moves into view, pick it up in the viewfinder and continue following. Then press the shutter release an instant before the subject reaches the point. If you wait until the subject gets there, it will be too late. You must anticipate.
When panning, it's possible to use any camera, any shutter speed and any film or ISO setting. BUT for best results, use a film no faster than ISO 100, or, on a digital camera, an ISO setting of 50, and a slow shutter speed such as 1/30 of a second or slower.
The reason for a slow shutter speed when panning is that the most dramatic effects are obtained if there's some blur in the background. A sharp subject and a blurry background add greatly to the impression of motion. With a shutter speed of 1/15 or 1/4, results can be very dramatic.
When using a digital camera, always be aware of lag time (the delay between the time the shutter release is pressed, and the time that the shutter opens). For best results, press the shutter release part way down to lock in the exposure, and press it the rest of the way an instant before you want to take the picture. Lag time makes it more difficult to anticipate the precise instant, but with practice it can be done.
If the subject has moving parts, such as the arms and legs of a runner, panning with a slow shutter speed can result in some extraordinary effects, but only if the subject is followed precisely. Arms, legs and background will be blurred, but the head and body of the subject will be sharp. Panning requires a lot of practice to be perfect, but the results are well worth it.
In an event such as night football or indoor hockey, or even a field of blowing grain, motion can be implied with extreme blur. Detail will be obscured, but the impression of the subject will still be retained. In fact, this type of photo usually has a distinct impressionistic quality. This is often much more dynamic than an action--stopping photo.
Extreme blur is similar to panning in that a slow shutter speed (and slow film or low ISO setting) should be used, and it often helps if something in this shot is sharp to provide a point of reference. One difference is that when going for blur, there is total disregard for following the action. For best results when a blurry shot is wanted, use a tripod, especially when there is a possibility that something in the picture might be motionless.