Hello guys, I am not sure whether this is actually a simple problem but I'm not really a physics student, just someone very passionate for it. So I'm trying to use newton's second law in its relativistic version (force is equal to the rate of change in momentum) to find the velocity and acceleration of a particle after a discrete period of time t. My difficulty arises because the velocities are present in the gammas, so I tried solving by substitution but it ended being really messy. So my problem is to get the final velocity (or the acceleration, of course) of a particle given the force acting on it, its initial velocity, position and acceleration, and its mass, using discrete quantities and in three dimensions. Should I be using four-vectors? Relevant formulae: F = dp/dt (should actually be deltas as i'm looking at the discrete case) p = m*v*gamma gamma = 1 / sqrt(1 - v2/c2) I would appreciate any help you can give me, even if it is just pointing in the right direction. Thanks in advance.