What does the physical problem S(t)V(t) a(t) mean about derivatives?
S(t), V(t) and a(t) are respectively the functional relations of displacement, velocity and acceleration at time t, and the first derivative of S(t) is V(t). The second derivative of S(t) or the first derivative of V(t) is a(t). The derivative of a(t) has no physical meaning, but it has mathematical meaning.