Reference System (Meaning and Explanation)

We explain what a reference system is in physics, what it is for and its different conceptions in classical and relativistic mechanics.

reference system dimensions depth height length — A reference system can have from one to four dimensions.

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What is a reference system?

When we talk about a reference system, we normally refer to a set of conventions that an observer needs, within a mechanical physical system, to be able to measure the position and other physical magnitudes of an object under study.

This means that a reference system is the context necessary to understand the dimensions and orientations of an object . For example, if we look at a photo of a dinosaur bone, it is impossible to know how big it is if we lack scale. That is why rules or objects are placed next to them, to establish a comparison. The latter is a reference model for size.

However, the appreciation of this concept in physics depends on the specific perspective from which it is studied:

In classical mechanics. The reference system is understood to be the orthogonal coordinate system with which we can study a Euclidean space, as occurs in analytical geometry. For example, the axis of coordinates that make up the meridians and parallels with which we imaginatively organize our planet, allow the construction of a global reference system that today we know as GPS (Global Positioning System) and that uses these imaginary lines as a reference to locate a point within the globe.
In relativistic mechanics. By reference system we understand the spatio-temporal coordinates that identify any physical event of interest, based on four orthonormal reference vectors: three spatial (height, length, depth) and one temporal (time).

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Reference system example

point of view reference system — Without a reference system we can confuse the dimensions of objects.

A simple and classic example to understand the use of reference systems is presented from a spaceship taking off of the Earth's surface.

For those who observe it from the surface, the ship ascends and soon it disappears from sight, looking smaller and smaller as it moves away. Instead, For the pilot it is the Earth that is left behind moving away from the ship and becoming smaller as it is left behind. For both of them this movement will be fast and linear.

But for a third spectator located in the Moon rocket movement may appear slow and distant minimal, barely occurring, and will only gain speed as it approaches it in its trajectory. This difference is due to the fact that a different reference system is used in each case.