S is that very small distance. It is the deflection distance or thickness of the cushioning. It is very difficult to determine but the starting velocity is also difficult to determine. A falling object has a known velocity based on the acceleration of gravity but a horizontally moving object requires some sort of metering of the horizontal speed. A slow walking speed of 3 mph is 134 cm/sec. 134 squared is 17956. If there is 1 mm (.1 cm) deflection, then you would divide the 17956 by .2 divided by 980 cm/sec/sec to get 91.6 G's. If the deflection was 1 cm, then you would divide that by 2 (2 times deflection of 1 cm) and the G force would be 9.16 G's. If the deflection was .25 cm then the G force would be 36.32 G's.

If the 3 mph speed (134 cm/s) was not directly at the wall, you would need to calculate the velocity vector perpendicular to the wall. At 45 degrees, the speed perpendicular to the wall would be 2.1 mph (94 cm/s). At 1 mm (.1 cm) deflection, then, 8798 divided by .2 divided by 980 is 44.9 G's. You need to make sure everything is in the same units: meters, centimeters or millimeters.