for i in range(nsteps-1):
    F_air[i+1] = (-b*V[i,0],0,-b*V[i,2])
    F[i+1] = F[i]
    V[i+1,:] = V[i,:] + F[i,:]*dt + F_air[i,:]*dt
    X[i+1,:] = X[i,:] + V[i,:]*dt
    if X[i,2] < 0:
        break

pl.plot(X[:,0],X[:,2],'o')
pl.title('A Falling Ball')
pl.xlabel('X Distance')
pl.ylabel('Height')