Ok so I know by using a neutral density filter you can lower you shutter speed as low as you like while keeping your aperture at a resonable level of around f/22.

I know that this will achieve motion blur and I know it works great when photographing water.

But I'm not sure if it will work in the situation I want to use it for. I will be using a 20mm wide angle lens to photograph a model in a busy city and I want a lot of movement and some motion blur in the background but I want the model to stay relatively sharp as the shoot is more about what she is wearing more than anything else.

If I use this technique of lowering the shutter speed and adding the ND filter will it work? Can someone just tell me if it will work or if I am completely wrong and should keep thinking. THANKS!