\frac{d^2 \overrightarrow{p}}{dt^2} = - K (m_A+1) \frac{ \overrightarrow{p}}{p^3} - K m \Big{(} \frac{ \overrightarrow{r}}{r^3} + \frac{ \overrightarrow{\Delta}}{\Delta^3} \Big{)} et m_A<<1 donc \frac{d^2 \overrightarrow{p}}{dt^2} = - K \frac{ \overrightarrow{p}}{p^3} - K m \Big{(} \frac{ \overrightarrow{r}}{r^3} + \frac{ \overrightarrow{\Delta}}{\Delta^3} \Big{)}