Static force, such as the weight of a person standing motionless on a bathroom scale or the force that an office full of equipment exerts on a high-rise floor, can be easily determined using scales, balances, load cells, and the like because static force doesn’t change over time. It’s straightforward to calibrate such devices with an unvarying force such as gravity acting on a known mass.

However, testing for dynamic force—such as automobile crash testing, fatigue testing of materials, and the changing forces applied during machining—has traditionally been difficult to measure because dynamic force changes continuously as it is applied. In many applications, a time-varying force causes large errors in instruments calibrated to measure static force. It is thus necessary to calibrate the response of these instruments to dynamic forces.

To meet that need, NIST scientists have devised the Kibble Dynamic Force Reference (KDFR), a traceable, dynamic force source based on the same principle used in a Kibble balance to generate an exactly known static force to counterbalance the weight of an unknown mass.

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