Exercise: Panning with different shutter speeds

Once again a scene with movement had to be chosen, for this excersise the movement had to be followed with the camera (panning) to try and capture the subject sharply whilst streaking the background to give a sense of movement. A series of photographs were taken with the shutter speed decreasing for each shot.
After trying unsuccesfully to photograph cars at speed I decided to change tactics and get my wife to ride her bike past me, panning is not something I had done before and I was surpised and pleased with the results.

Photograph1  1/1000  f5.6
The subject and background are sharply frozen

Photograph 2  1/500  F8
The subject and background are still sharply frozen

Photograph 3  1/250  F13
The background focus is not as sharp, signs of movement are appearing with the faster moving parts of the subject.

Photograph 4  1/125  f18
More background blur, more movement to the wheels and feet.

Photograph 5  1/60  F25
Background is blurred, more movement .

Photograph 6  1/30  F29
As 5

Photograph 7  1/15  F29
Subject has now taken on appearence of momentum, background streaked.

Photograph 8  1/6  F29
Struggling to keep subject in focus, lots of streaking

Photograph 9  0.6  F29
Shot shows distance travelled in 0.6 of a second

Another enjoyable exercise and something I will be practising again soon. Again I had trouble with over exposure at the slow shutter speeds, probably need to get a filter to help with this.
Of all of the pictures I like number 7 the best, I like the way that the subjects movement is enhanced and appears to have been 'lifted' from the background, and the way the background streaking adds to the 'speed' effect.