RK2 Method:

x_n+1 = v_n+1/2 dt + x_n

v_n+1 = a_n+1/2 dt + v_n

x_n+1/2 = v_n dt /2 + x_n

v_n+1/2 = a_n dt /2 + v_n

with dt = t_n+1 - t_n