This exercise (p34) is to demonstrate the effect shutter speed has on the perception of movement in a static photograph. Slower shutter speeds will blur the moving parts giving the illusion of movement whereas faster shutter speeds will freeze the action.
Here is my series of photographs of some little birds hand feeding. The hand is static in each photo because it is not moving but the birds are blurred and get less blurred as I increase the shutter speed.
Shutter Speed: 1/60 sec. Notice how the bird is moving so fast the slow shutter has blurred it into a brown smudge.
Shutter Speed: 1/80 sec. You can see the birds this time but the one bird that is still moving is almost completely blurry.
Shutter Speed: 1/100 sec. Slightly better than 1/80th but still too slow.
Shutter Speed: 1/125 sec. This is the one. The moving birds are now only blurred in the wings, showing a nice amount of movement but their faces are in focus.
Shutter Speed: 1/160 sec. If we keep going, increasing the shutter speed, we can now see the downward stroke of the moving birds wings which is less pleasing that the faster movement above. The faster movement gives more of a feeling of fast little birds.
Shutter Speed: 1/250 sec. In this one the wings are *almost* frozen in time, you can at least see the whole outline of their little wings. This might be a nice sort of blur to have on a bigger bird to suggest a huge slow wingspan beat or something like that but less appropriate for these little guys.
OCA Art Of Photography 