Some more flash duration testing this time with Bear as the model.
When using natural light you can freeze action by using a fast shutter speed. When using a strobe (and low ambient light) you freeze action with the light from the strobe rather than the shutter. The length of the pulse of light that comes out of the strobe is the flash duration. The shorter the flash duration the cleaner the image as you will get less blur.
In these shots I threw a dog biscuit with one hand and pressed the shutter with the other. Bear is quite happy to work for food.