Probably thinking of https://en.wikipedia.org/wiki/Jerk_(physics) https://en.wikipedia.org/wiki/Jerk_(physics) If acceleration were an instantaneous off-on ste

Probably thinking of https://en.wikipedia.org/wiki/Jerk_(physics) https://en.wikipedia.org/wiki/Jerk_(physics) If acceleration were an instantaneous off-on step, that would be a https://en.wikipedia.org/wiki/Dirac_delta_function https://en.wikipedia.org/wiki/Dirac_delta_function