4-velocity --> 4-acceleration? Hey all, my first post here. Now, Im trying to derive the 4-acceleration from the 4-velocity by explicitly calculating du/d(tau). So from Hartle we have u=( gamma, gamma*v) where gamma=1/Sqrt(1-v^2) and v is the 3 velocity, taking c=1 So then, du/d(tau)=( d(gamma)/d(tau), d(gamma*v)/d(tau) ) from the book we have du/d(tau)=(gamma*(a dot v), gamma*a) so then we should have d(gamma)/d(tau)=gamma*(a dot v) but when i calculate d(gamma)/d(tau) i get....ok im going to show all my steps so people can know what ive done.... d(gamma)/d(tau)=[d(gamma)/dv)]*[dv/dt]*[dt/d(tau)] =[d(1/(1-v^2)^(1/2))/dv]*[a][gamma] =[(-1/2)(-2*(v)/(1-v^2)^(3/2)]*[a]*[gamma] =[ va/(1-v^2)^(3/2)*[1/gamma] =v*a*gamma^4 != v*a*gamma does anyone know whats going wrong or what im doing wrong?? Any help would be appreciated, Thanks in advance.