1. The problem statement, all variables and given/known data Hi there, I wish to use Newton's Laws in conjunction with Euler's Method to model the motion of a planet around a star. 2. Relevant equations 2nd Law F = m*a Law of Universal Gravitation F = -G*M1*M2/r^2 3. The attempt at a solution First I combined the two laws above. m*a = -G*M1*M2/r^2 Where M1 cancels out. a = -G*m/r^2 Rewriting a as the second derivative of position gives: d^2r/dt^2 = -G*m/r^2 Euler's method is incompatible with a second order differential equation, so I tried to write it as a system of coupled first order differential equations. dr/dt = v and dv/dt = -G*m/r^2 I guess this is where I'm a little stuck. Does everything appear correct so far? I tried Euler's method on these two but I think my results were incorrect. Any help would be greatly appreciated.