What does this paragraph mean?

[M. next]

Components of angular momentum are also conserved in the case of a system evolving in an external conservative field with spherical symmetry where the resultant of all forces is radial i.e potential energy of the system depends only on radial coordinate.

 

[Steely Dan]

For example, if you have a planet orbiting the Sun (assume the Sun is stationary), then angular momentum of the planet is constant, since the potential energy of gravity is only a function of the distance from the Sun (i.e., it is spherically symmetric).

 

[M. next]

Thanks. that was short and to the point.

 

[genericusrnme]

Components of angular momentum are also conserved in the case of a system evolving in an external conservative field with spherical symmetry where the resultant of all forces is radial i.e potential energy of the system depends only on radial coordinate.

in lagrangian langange it's saying that the angular degree of freedom is cyclic
in physics language it's saying that if there's no force acting on the angular degree of freedom then nothing about the angular degree of freddom will change

remember that force = gradient . potential energy, if the potential energy only depends on the radial coordinate then any change in the angular coordinate will make no change in the potential energy, so there is no 'angular forces'.