We know the following basics.
Velocity(V) = (Change in Distance)/(Time)
Accelaration(a) = (Change in Velocity)/(Time)
Change in distance is denoted by 'y' and time is represented by 't'.
`V = (dy)/dt`
`a = (dV)/dt = (d(dy/dt))/dt = (d^2y)/(dt^2)`
`a = (d^2y)/(dt^2)`
y = represent distance/displacement which is a vector
t = time
d = this means the derivative. This is used to represent the change of velocity and displacement with time.