In a recent comment published in this journal (2015 Eur. J. Phys. 36
[http://dx.doi.org/10.1088/0143-0807/36/3/038001] 038001 ), Khrapko derived the relationship between
coordinate acceleration and coordinate speed for the case of radial motion in Schwarzschild
coordinates. We will show an alternative derivation based on the Euler–Lagrange formalism. The
Euler–Lagrange formalism has the advantage that it circumvents the tedious calculations of the
Christoffel symbols and it is more intuitive. Another aspect of our comment is that one should not
give much physical meaning to coordinate dependent entities, GR is a coordinate free field, so, a
relationship between two coordinate dependent entities, like the acceleration being dependent on
speed, should not be given much importance. By contrast, the proper acceleration and proper speed,
are meaningful entities and their relationship is relevant. The comment is intended for graduate
students and for the inst…