So we could either view this as the second derivative, we're taking the derivative not once, but twice of our position function, or you could say that we're taking the derivative with respect to time of our velocity function. So this is going to be, we can write this as dv dt, the rate at which velocity is changing with respect to time, and what's another word for that? Well, that's also called acceleration. This is going to be our acceleration as a function of time. So you start with the position as a function of time, take its derivative with respect to time, you get velocity. Take that derivative with respect to time, you get acceleration. Well, you could go the other way around.