In two we can define a soft collision:
1) A collision depends on the kinetic energy transferred and is therefore linked to the duration in which it occurs. When the duration is extended, the value of the momentum also decreases. Change in momentum will be begative when the final velocity is lesser than the initial velocity just before the impact with mass as constant.
2) For the particular case of the forces. These tend to decrease dramatically. Basically, the impact is not carried out instantaneously, but is diminished and lethargic by means of the bags at a higher level. This physically allows anyone who may have received damage to be suspended first in a few thousand more times in order to reduce the strength they receive. This could be clearly seen in a Force vs. Time graph, in the comparison of the airbags and without them.