Impressionist painters were more concerned with colour than line. Their goal was to leave the viewer with an impression of the scene rather than a literal depiction and their works often included a sense of movement.
Photographers can also create emotional abstracts that leave only an impression of the original subject by using a slow shutter speed, from 1/50 of a second to 1/2 second, and moving the camera while the shutter is open or allowing a moving subject to pass in front of the camera.
This technique is fun because every frame turns out different. An afternoon can easily slip by as if moving on the waves of colour. There are 3 ways of approaching this technique:
1. Pan with a moving subject
When you move the camera while the shutter is open, it is called panning. With a moving subject, you want to pan at the right speed to keep the subject in the frame. Panning on a moving subject with a very slow shutter speed has a drastically different result than panning with a faster shutter speed. A faster shutter will have more sharpness in the subject and show some blur in the background. A very slow shutter speed is more abstract and allows you to really feel the movement while retaining just enough detail in the subject that you can still tell what it is.