In a 2-dimensional coordinate system, which of these is an example of an object's position?

A. east
B. (-2, 7)
C. southwest
D. 5 kilometers

' B ' is the only choice on the list that tells you a definite place, where you could go to pick up the object or meet somebody.

But in order to use it, you also have to know where the origin of coordinates is ... the point (0, 0) .

No, I'm wrong about that.  You have to know where SOME other point is, but that doesn't have to be (0, 0).

graph slopes whilst gas cools, then it is flat whilst conensation to liquid happens, the coolong liquid then graphs as a slope when it solidifies graph is flat

latent heat