physical science?

Question

how does a person determine a frame of reference?

Answer 1

The question is a bit vague, but I will try to give a meaningful answer to it.

When studying a movement, we typically choose the frame of reference which will make the movement the simplest possible. When observing a ball bouncing on earth, you will typically choose yourself as a frame of reference because the movement will usually be simpler to analyze in your own frame of reference.

Suppose you were studying the movements of the solar system's planets. If you pick you (earth) as the frame of reference, you will find that the planets of the solar systems will describe very complicatedly shaped trajectories that are difficult to analyze mathematically and to predict. If you pick our sun as the reference frame however, you quickly notice trajectories simplify a lot and are treated much more easily. This is due to the fact that compared to the gravitational attractions exerted by planets outside the solar system (remember gravitational attraction fades off like 1/r^2, where r is the distance), the sun's gravitational attraction is by far the most dominant and significant one. Therefore the behavior of these planets is most influenced by it and it is convenient to pick the sun as a reference frame for all our intents and purposes.

If we were however to study the movements of other suns in our galaxy, we would find that they are much easier to analyze and predict by taking as a reference frame the center of the galaxy, rather than our sun, for the same reasons as above.

So there is no "right" reference frame for any given situation. We would usually choose the one which gives us the simplest movement. For movements on earth, of relatively short duration, the earth frame of reference is sufficient. When the duration of a movement and its nature is such that the distance it travelled around the earth's axis is significant, we would choose the geocentric frame of reference. For movements of satellites, we generally pick the planet around which the satellite is rotating as a frame of reference. For movements of planets in the solar system, we would typically pick the sun and so on.

Good luck for your studies !