The discussion revolves around the possibility of calculating the mass of the Milky Way using only the speed of a planet (or star) in a circular orbit. Participants explore the relationship between orbital speed and mass within the context of gravitational forces and circular motion.
The conversation is ongoing, with participants examining the implications of missing information and the feasibility of assumptions. Some guidance has been offered regarding the relationship between forces in circular motion, but no consensus has been reached on how to proceed without the radius.
There is a noted absence of critical values such as the radius of the orbit or the period of the orbit, which participants agree complicates the problem. The original poster expresses confusion over the lack of these details.
SHISHKABOB said:well there's only one force acting on a something out in space (most of the time, let's just assume this is the case)
so if Fnet = Fg
can you take it from there?
Exactly. If you don't have the radius, then you can't get the speed. You would need to find the radius some other way, or introduce other assumptions.fawk3s said:Well, in a circular orbit,
Fcentripetal=Fg
You are given only the speed v. The problem is how to get rid of the radius (r). Dunno how, and if possible.
BruceW said:for example, you could assume that the star fits the typical trend of other stars in orbit around the milky way, then you could work out the radius of the star.