Panning with different shutter speeds

Having found an appropriate spot between two posts (kept out of shot) and a willing subject, I got my daughter, Amber to run back and forth between the posts. I started at a slow shutter speed of 0.4sec as I knew that this would create a good blur and slowly worked my way up.
My starting shot shows a green blur and a mass of arms, legs and heads all morphing into each other. It shows a great sense of movement and the cooling tower in the background has completely disappeared.
Shot two (1/4sec) has caught a little more detail, the body is slightly more defined while there still appear to be multiple limbs.
In shot three (1/5sec) we only have one of each limb, although very blurred, yet the right foot still has multiples.

By shot four (1/8sec) the torso, although still a little blurred is easily distinguishable while the feet are still showing a lot of movement. The cooling tower in the background has now come into view. Shot five (1/15sec) is pretty similar but slightly more defined.

By shot six (1/30) we can clearly see the face and torso, even down to creases on the jacket. The feet now look like feet yet they still have a fair amount of motion blur. On shot seven (1/60), Amber doesn’t look much more in focus than in the previous photo, however the main difference is in the background. The cooling tower is much more clear and the steps up the side of the large tank are now visible.

By my final photo (1/125), Amber was getting pretty tired and I thought I was finished. Having uploaded the photos to my laptop, I now realise I could have gone further. Amber’s feet still have some motion blur and at a faster shutter speed, the grass in the background would have also looked much sharper.

We could return to the setting in order to complete the assignment in the future, however I don’t think it is worth it from an aesthetic point of view. I feel that for this type of shot, a certain amount of motion blur is necessary in order to show movement so any further shots with quicker shutter speeds would be much less pleasing to the eye.
My favourite shot of the set is shot two (1/4sec) as I like the effect of seeing a fairly solid torso with the spinning limbs. I also like shot six (1/30) as Amber’s image is fairly sharp, yet the background is still blurred enough to show movement.