The above states that the velocity of point Q relative to P is represented by dr/dt. However, it also states that ∂r/∂t is the apparent velocity of Q in Pxyz. How does that make sense? I mean P is the origin of axes Pxyz so surely the velocity of point Q relative to P should be the same as the apparent velocity of Q in Pxyz? Also, slightly unrelated to the above, what is the exact difference between a frame of reference and an axis? My lecturer uses them interchangeably but I suspect there is a difference. I'm a layman when it comes to this topic and my lecturer hasn't explained this whole topic very well so I'd appreciate it if someone could simplify.