Inertial Frame Of Reference

In Physics especially were motion is concerned you will often hear the term "Inertial Frame of Reference" or "Inertial Reference Frame", but what is it? Well, technically it can be described as follows (this one is taken from Wikipedia);


In physics, an inertial frame of reference (also inertial reference frame or inertial frame or Galilean reference frame) is a frame of reference that describes time homogeneously and space homogeneously, isotropically, and in a time-independent manner.

All inertial frames are in a state of constant, rectilinear motion with respect to one another; they are not accelerating in the sense that an accelerometer at rest in one would detect zero acceleration.

It goes on to say

Measurements in one inertial frame can be converted to measurements in another by a simple transformation (the Galilean transformation in Newtonian physics and the Lorentz transformation in special relativity). In general relativity, in any region small enough for the curvature of spacetime to be negligible one can find a set of inertial frames that approximately describe that region.

Glad we cleared that one up! See this can sometimes be the problem with Physics. In order to describe something in such a manner that it is not open to misunderstanding, misinterpretation or ambiguity you can end up sounding like a lawyer.  Worse, you write something that most people cannot understand! Let's be honest the definition above is a bit of a shocker. So, is there a way we can state it in plain English without losing fidelity? Can we describe the same thing in 2 words?  Let's have another look at what has just been said

an inertial frame of reference (also inertial reference frame or inertial frame or Galilean reference frame) - this section is just telling us what it is called. I'm going to call it "my garage".


describes time homogeneously and space homogeneously, isotropically, and in a time-independent manner. - tells us that time is uniform (a second is a second) and that space it is same in each direction and doesn't change with time. In the case of "my garage" the dimensions of the garage do not change over time, and an hour continues to be an hour, hour after hour.

All inertial frames are in a state of constant, rectilinear motion with respect to one another; they are not accelerating in the sense that an accelerometer at rest in one would detect zero acceleration. - everything is moving in a straight line at a constant speed (think of Newton's first law - ...an object in motion stays in motion with the same speed and in the same direction...), or does not appear to be moving at all, a bit like my garage.

So, a reasonable representation of an Inertial frame of reference is .... "Your garage".

Feel free to experiment in this garage and when publishing your results remember to start with ....

The experiments where carried out in an inertial frame of reference (also inertial reference frame or inertial frame or Galilean reference frame), ie a frame of reference that describes time homogeneously and space homogeneously, isotropically, and in a time-independent manner.

This inertial frame was assumed to be in a state of constant, rectilinear motion with respect to any other inertial reference frame; it was not accelerating in the sense that an accelerometer at rest in the inertial frame would detect zero acceleration.


 or you could say you did them in your garage.