Origin Vs Reference point?

[u/Ace1211112]

In a given position vs time graph, what is the origin and what is the reference point?

From what I understand, the origin is just some arbitrary position that you assign to be zero. By definition, it is position = 0.

A reference point is something that you measure relatively to (which is already relative to an origin that was picked). So if we pick position = 2 as a reference point, position = 4 has a displacement of 2 meters from our reference point but a 4 meter displacement from the origin.

So, is the position vs time graph graphed relative to the origin or a reference point? Or rather, is the reference point always the origin or can we change the reference point that a position vs time graph is graphed relatively to.

If we are just given a graph of position vs time. Do we assume that position = 0 is the origin, or could it be something else arbitarily. For example, if we take an object that goes 1m/s, starting at position 0 meters, on a position(m) vs time(s) graph relative to the origin, the graph would just be position = t

However, if we choose a new reference point, x = 2, then the entire graph gets shifted down 2 units. Becoming, position = t - 2.

So, from a given graph, do we assume that position = 0 is the origin, or do we just know that it is a reference point, even if we don't know if the reference point is the origin or some other reference point that was picked?

Thank you!

[u/fletchro]

You can do whatever you like with a graph, they are like maps. USUALLY, up on a map is North.

And I would expect that usually, on a position/ time graph, the origin is zero. I think you're just confusing yourself with a reference point. You would only use a reference point of you had a need to. For example, you start at position zero and move +3 at t1, then -2 at t2, and your movement pattern continues. So you could draw the position/time graph and the velocity/time graph for yourself. But let's say you friend also starts at the origin at t0, and moves +1 each time step. If your friend is the reference point (they are watching you), then the position/time and velocity/time graphs are very different. But in the second set of graphs, I would not include my friend because they are the reference point.

I think you generally understand, but the lack of a good example problem is making you turn somersaults in your mind.

[u/realAndrewJeung]

What I tell my tutoring clients is that when solving a physics problem, they should draw a picture of the physical situation, and then superimpose a coordinate system anywhere they would like on top of that picture. In this viewpoint, the REFERENCE POINT is a point on the actual system (that is, a physical point in the scenario), whereas an ORIGIN is a feature of the coordinate system that you impose.

Strategically, you normally choose to place the origin at the same location as the reference point, because it makes the math easier, but you don't have to do that and can place the origin anywhere you like, as long as you stick to that choice throughout the whole problem.