Degree of freedom of two point mass

[orienst]

If I have two point mass moving on a track, we say that this system has 2 degrees of freedom, because we need two independent variable to locate the point mass. But what’s the number of DOF if their (the two point mass) distance was determined? Is it one? If so, which variable can locate the two point mass?

 

[AJ Bentley]

I think you are asking about measuring the distance between the masses?

If you do that, you can say there is only one d.o.f.
BUT, only if you use a frame of reference that is based around the centre of mass.

Any other frame will require two, the distance between them and the position of the centre of mass.