Originally Posted by tusenfem

Suppose you have a car driving on the street and you are standing on the pavement with your new digital SLR camera. Now you can do two things with that camera:
1. you can take a pic with a very short exposure time, you can see the car clearly, and determine its location very well, however, you have no information about the speed of the car.
2. you can take a pic with a long exposure time, you will see a very blurred car, stretched over the picture, so you can determine the velocity of the car rather well, but any information about the exact location of the car is lost.