http://www.ebay.co.uk/itm/Canon-EF-5...item27bfc7da69
Flash is a difficult balance - the flash freezes anything it hits no matter what your shutter speed is - as long as the light from the flash overpowers the ambient light.
The ambient light is controlled with the shutter speed - the flash is controlled with the power of the flash along with the aperture / iso. It's of course more complex than that, but that's a loose rule to consider.