# Reference frames A **reference frame** is a physical concept grounded in physics, representing a perspective or point of view from which measurements are made. It can be thought of as a velocity and position in space from which to observe things. It provides both a physical perspective for observations and a mathematical framework for describing positions and motions. The choice of reference frame can significantly affect how motion and other physical phenomena are perceived and measured. ### Types of Frames of Reference There are two main types of reference frames: 1. **Inertial Reference Frames** * These are frames of reference that are either at rest or move at a constant velocity. * In an inertial frame, an object not acted upon by a force will continue to move at a constant velocity (or remain at rest) according to Newton’s first law of motion. * The laws of physics, including the principle of relativity, hold true in all inertial frames. Special relativity is primarily concerned with inertial frames. 2. **Non-Inertial Reference Frames** * These frames are accelerating or rotating. * In a non-inertial frame, additional fictitious forces (such as centrifugal force or Coriolis force) must be introduced to apply Newton’s laws correctly. * Examples include a rotating carousel or an accelerating car. ### Creating a Reference Frame We can create a reference frame as follows: consider a single [Observer](Observer.md) who doesn't accelerate in any way and use them to set up a [Coordinate System](Coordinate%20System.md). They have clock with them, so we can use the [Proper Time](Proper%20Time.md) along their trajectory to define a time coordinate $t$. We also image that once every second our [Observer](Observer.md) shoots out "infinitely fast" rays in all directions. We all know nothing can travel infinitely fast, so this is a purely conceptual move. ### Reference Frames, [Coordinate Systems](Coordinate%20System.md), [Observers](Observer.md) A reference frame is physical and related to observing phenomena, while a [Coordinate System](Coordinate%20System.md) is a mathematical construct for describing positions. An [Observer](Observer.md) uses a reference frame to make measurements, and may employ various [Coordinate Systems](Coordinate%20System.md) to express those measurements. You can have different coordinate systems for the same reference frame, but changing reference frames implies a change in the physical perspective of observation --- Date: 20240630 Links to: Tags: References: * []()