the lower the apeture number, the more light is let in, therefor in theory, a faster shutter can be used, and the opposite is true.
not too familiar with the s100, whether or not it has apeture/shutter priority or not (what PliotronX was explaining i do believe). Flip thru they manual (throw away that ego and just use it 😛) and see if there's anything about "fast shutter" mode or something like that. the s10 i know had that setting.