FIGURE 7-1 Effective momentum of high-rate ballistic impacts at muzzle velocity and low-rate football impact. SOURCE: Cameron Bass, Duke University.

This difference between conventional blunt trauma and ballistic blunt trauma is emphasized by considering typical timelines for ballistic impact. The need to decelerate an incoming round from hundreds of meters per second to zero over a span of centimeters implies a relatively rapid interaction between the head and the deforming helmet. A typical interaction timeline is shown in Figure 7-2.


FIGURE 7-2 Ballistic impact injury timescales. SOURCE: Bass et al., 2003.

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