Content deleted Content added
m Task 5: Fix CS1 deprecated coauthor parameter errors |
|||
Line 9:
A reference frame is a physical system in which physical quantities are defined, such as position, momentum, spin, time, etc. Some obvious examples of reference frame are metre stick for distance and clock for time. While some standards are widely accepted and used like the [[Metric system|metric]] and [[imperial units|imperial]] system, there is no constraint on what physical system a reference frame has to be, so it is perfectly valid, though peculiar, to use Tom Cruise (who is 1.70m high) as a reference frame and to describe Katie Holmes as 1.029 Tom Cruise high. Regardless of what reference frame is used, it is always relational, not absolute.
When speaking of a car moving towards east, one is referring to a particular point on the surface of the Earth; moreover, as the Earth is rotating, the car is actually moving towards a changing direction, with respect to the Sun. In fact, this is the best one can do: describing a system in relation to some reference frame. Describing a system with respect to an absolute space does not make much sense because an absolute space, if it exists, is unobservable. Hence, it is impossible to describe the path of the car in the above example with respect to some absolute space. This notion of absolute space troubled a lot of physicists over the centuries, including Newton. Indeed, Newton was fully aware of this stated that all inertial frames are [[Observational equivalence|observationally equivalent]] to each other. Simply put, relative motions of a system of bodies do not depend on the inertial motion of the whole system.<ref name = "Dickson">{{cite journal|doi = 10.1016/j.shpsb.2003.12.003|last = Dickson|first = Michael|title = A view from nowhere: quantum reference frames and uncertainty| journal = Studies in History and Philosophy of Modern Physics | volume = 35|issue = 2 |year = 2004 |pages = 195–220}}</ref>
An [[inertial]] reference frame (or [[inertial frame]] in short) is a frame in which all the physical laws hold. For instance, in a rotating reference frame, Newton's laws have to be modified because there is an extra Coriolis force (such frame is an example of non-inertial frame). Here, "rotating" means "rotating with respect to some inertial frame". Therefore, although it is true that a reference frame can always be chosen to be any physical system for convenience, any system has to be eventually described by an inertial frame, directly or indirectly. Finally, one may ask how an inertial frame can be found, and the answer lies in the [[Newton's laws]], at least in [[Newtonian mechanics]]: the first law guarantees the existence of an inertial frame while the second and third law are used to examine whether a given reference frame is an inertial one or not.
| |||