NASA researchers have conducted an instrumented hammer test to measure the force and response of a structure. The study found that a half-sine waveform is not the only idealized input for such tests. In fact, the actual force applied can be more complex, with crest ripples and separated contacts that can affect the outcome. The researchers emphasize that the adequacy of the test depends on the accuracy of the measurements, the signal-to-noise ratio, and the coverage of the test objective. The study highlights the importance of understanding the spectral content of the measured force history, which can be influenced by the timing between separated contacts and the presence of crest ripples. The researchers recommend that test adequacy should be evaluated against the intended objective, taking into account the measured force and response signals. The findings of this study have implications for modal analysis and pyroshock testing, where accurate force and response measurements are crucial for obtaining reliable results. By understanding the limitations of hammer-tap inputs, researchers and engineers can design more effective tests and improve the accuracy of their results.