Everything about Inertial totally explained
An
inertial frame of reference, or
inertial reference frame, is one in which is valid, the
law of inertia.
Newton viewed the first law as valid in any reference frame moving with uniform velocity relative to the fixed stars; that is, neither rotating nor accelerating relative to the stars. Today the notion of "
absolute space" is abandoned, and an inertial frame is defined as:
An inertial frame of reference is one in which the motion of a particle not subject to forces is a straight line. |
Hence, with respect to an inertial frame, an object or body
accelerates only when a physical
force is applied, and (following
Newton's first law of motion), in the absence of a net force, a body at
rest will remain at rest and a body in motion will continue to move uniformly—that is, in a straight line and at constant
speed. It is useful to picture this situation as if we're situated in a zero-gravity condition, but it isn't impossible to establish an inertial frame in which gravity exists. For example, an observer confined in a free-falling lift will assert that he himself is a valid inertial frame, even if he's accelerating under gravity, so long as he's no knowledge about anything outside the lift. So, strictly speaking, inertial frame is a relative concept. With this in mind, we can define inertial frames collectively as a set of frames which are stationary or moving at constant velocity
with respect to each other, so that a single inertial frame is defined as an element of this set.
Equivalence of inertial reference frames
The basic
principle of relativity states: "Only
relative motion is observable; there's no absolute standard of rest". According to this principle, the
Laws of Physics are the same in all inertial frames (otherwise the differences would set up an absolute standard). In practical terms, this
equivalence of inertial reference frames means that scientists within a box moving uniformly can't determine their absolute velocity by
any experiment.
By contrast, bodies in
non-inertial reference frames are subject to so-called
fictitious forces (pseudo-forces); that is,
forces that result from the acceleration of the
reference frame itself and not from any physical force acting on the body. Examples of fictitious forces are the
centrifugal force and the
Coriolis force in
rotating reference frames. Therefore, scientists within a box that's being rotated or otherwise accelerated (except by gravity)
can measure their
acceleration and
angular velocity by observing the motion of an un-restrained body inside the box.
Inertial frames in Newtonian mechanics
Classical mechanics, which includes relativity, assumes the equivalence of all inertial reference frames.
Newtonian mechanics makes the additional assumptions of
absolute space and
absolute time. Given these two assumptions, the coordinates of the same event (a point in space and time) described in two inertial reference frames are related by a
Galilean transformation
»
From this perspective, the
speed of light is only accidentally a property of
light, and is rather a property of
spacetime, a
conversion factor between conventional time units (such as
seconds) and length units (such as
meters).
Einstein’s general theory of relativity
Einstein’s
general theory modifies the distinction between nominally "inertial" and "noninertial" effects by replacing special relativity's "flat"
Euclidean geometry with a curved
non-Euclidean metric. In general relativity, the principle of inertia is replaced with the principle of
geodesic motion, whereby objects move in a way dictated by the curvature of spacetime. As a consequence of this curvature, it isn't a given in general relativity that inertial objects moving at a particular rate with respect to each other will continue to do so. This phenomenon of
geodesic deviation means that inertial frames of reference don't exist globally as they do in Newtonian mechanics and special relativity.
However, the general theory reduces to the special theory over sufficiently small regions of spacetime, where curvature effects become less important and the earlier inertial frame arguments can come back into play. Consequently, modern special relativity is now sometimes described as only a “local theory”. (However, this refers to the theory’s application rather than to its derivation.)
Further Information
Get more info on 'Inertial'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://inertial_frame_of_reference.totallyexplained.com">Inertial frame of reference Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
