Applied forces launch bending waves because they produce both lateral and longitudinal displacements
Evidence
It is difficult to generate pure shear waves in a plate via the use of applied forces because in practice an applied force results in both lateral and longitudinal displacements. This has the effect of launching bending (flexural) waves into the plate. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 121
Categorization
Category: Causal Relationships