From my physics class manymany decades ago -
Position is also known as displacement
Rate of change of displacement per unit time (1st derivative) = velocity
Rate of change of velocity per unit time (2nd derivative) = acceleration
Rate of change of acceleration per unit time (3rd derivative) = jerk (I am not making this up...)
If you're braking w/ constant negative acceleration, then jerk = 0
But if you hit a slick spot so that acceleration suddenly goes to zero, then that's "positive jerk". Where you were against the tight shoulder straps, your torso now bounces back against the seat. This gives the PERCEPTION of positive acceleration!
