The first peak in a force-time or force-deflection curve obtained during an instrumented impact test. It arises from the inertia of that part of the test specimen (referred to as the contact mass) which is accelerated after the first contact with the striker (contact between specimen and striker can be temporarily lost). The peak force increases approximately linearly with increasing impact velocity, while the duration decreases. At impact velocities above 2 m/s, the duration is approximately constant but depending on the material being tested.