Should you shoot in Aperture Priority (Av) or Shutter Priority (Tv) mode? If you want to show any object in motion choose Shutter Priority (Tv) mode :
In the above picture I wanted to show light trails of cars in motion. So I chose Shutter Priority with a shutter speed of 8 seconds. As the shutter remains open for a bigger amount of time the camera has to be on a tripod to prevent it from shaking which will blur the image.
To freeze motion choose a faster shutter speed :
To freeze the motion of the butterfly I used a shutter speed of 1/100 second (0.01).
PHOTOMANTRA : Slow shutter speeds to blur motion.