frames of reference
So, I complained about MythBuster's explanation of relative velocity.  How would I explain this?  I would start by saying that velocity is relative.  Here is the definition for velocity:
I put the "avg" in there because it is more true.  If the acceleration is zero, I could drop this.  For the rest of this post, I am going to assume zero acceleration.  Ok.  But what is the r vector?  It is simply a vector from the origin to the object.  Here is a picture.
Simple, right?  And so the velocity tells how this vector r changes.  But wait.  Who says that I used the correct origin?  How do you…
