What is Reference: Definition and 1000 Discussions
Reference is a relationship between objects in which one object designates, or acts as a means by which to connect to or link to, another object. The first object in this relation is said to refer to the second object. It is called a name for the second object. The second object, the one to which the first object refers, is called the referent of the first object. A name is usually a phrase or expression, or some other symbolic representation. Its referent may be anything – a material object, a person, an event, an activity, or an abstract concept.
References can take on many forms, including: a thought, a sensory perception that is audible (onomatopoeia), visual (text), olfactory, or tactile, emotional state, relationship with other, spacetime coordinate, symbolic or alpha-numeric, a physical object or an energy projection. In some cases, methods are used that intentionally hide the reference from some observers, as in cryptography.References feature in many spheres of human activity and knowledge, and the term adopts shades of meaning particular to the contexts in which it is used. Some of them are described in the sections below.
in this text:
my question is in highlighted line:
"The two rods have the same length (in S) and contain the
same number of charges." why?
Considering that the negative rod has movement, it should have a shorter length than the positive rod according to a relativity!
TL;DR Summary: Reference request
Hello!
Reading the book "Differential geometry of Singular Spaces and Reduction of symmetry" by J. Sniatycki https://www.cambridge.org/core/books/differential-geometry-of-singular-spaces-and-reduction-of-symmetry/7D73498C35A5975594605428DA8F9267
I found that...
When an object is in freefall, it is in a locally inertial frame of reference. If two objects are in freefall, can their locally inertial frames of reference have different relative velocities?
This was a practice question, so it had the answer with it, which is 31 minutes. However, I'm confused as to why Lisa experiences T0. It isn't exactly an event happening in Lisa's rocket, but rather her just moving through space. From her perspective, it should look like Earth is moving at the...
Full code goes here: The goal of the program is to overload the extraction operator for cout.
#include<iostream>
using namespace std;class Time
{
private:
int hour;
int min;
public:
Time()
{
hour=min=0;
}
Time(int h,int m)
{
hour=h;
min=m...
TL;DR Summary: How do i find the intensity of this wave?
I know I is proportional to amplitude / frequency squared, but I don't know what equation this comes from. And I don't know how to answer this.
https://stackoverflow.com/questions/2685854/why-should-the-copy-constructor-accept-its-parameter-by-reference-in-c
I've read these answers, but most of them aren't satisfactory. They just throw a big wall of text. I get they're trying to say something about infinite recursion, but I'm failing...
I have a rocket and it is moving straight from a point P with a velocity ##v##. When I say that ##x'=0## is at the place we sit in the rocket, then when the event happened outside his rocket at the point P, can I say that the coordinate of the event is for him negative, so ##x'=-vt'##, although...
We have inhomogenous dirichlet boundary conditions (well understood)....the laplace equation is a steady state equation and we can clearly see that in 2D..it will be defined by 4 boundary conditions and NO initial condition...having said that; kindly have a look at the continuation below...
I...
Hi, there. I am currently reading the paper, Gravitational Faraday rotation induced by a Kerr black hole (https://doi.org/10.1103/PhysRevD.38.472). After Eq. (2.4), it reads that
The paper does not provide the derivation of the equations and no related reference is listed. Also, ##k^i## is not...
I have been thinking about the classic example of two twins traveling at different speeds and the effect of time passage. One twin that goes off to travel near the speed of light while the other twin is left on earth. We theorize that the traveling twin will pass through less time and be...
I'm using C# to program in Unity and I'm having some trouble with getting a tooltip box to update every frame.
Simplified, Class A (and several other classes and instances of classes) has a string that stores the tooltip text and updates it every frame.
Class B contains the logic to generate the...
what would be the y'-x' ##\vec r## vector be?
I think it is
##\vec r = (8t - 1) \hat i + (6t - 2) \hat j## (not sure whether it is correct or not.)
I thought about it as at t = 0 the position needs to be -1i -2j so that is why I took the signs in the y'-x' frame position vector as a - instead...
for (a): I basically got the correct answer, but when resolved with taking different reference lines/frames I got a different answer.
for the 1st attempt I took y = 0 (for both ##U_{el}## and ##U_{grav}) at the position where the spring is uncompressed.
for the 2nd attempt (with wrong solution)...
On May 31, 2022, the Daya Bay experiment announced in a press release that they had made a new ultra-precise measurement of the neutrino oscillation parameter theta13 (but did not provide the half line of text necessary to fully summarize the new result).
The press release also doesn't provide...
The Wikipedia references is
https://en.wikipedia.org/wiki/Recombination_(cosmology).
It says:
Recombination occurred about 370,000 years after the Big Bang (at a redshift of z = 1100),
and
the cosmic background radiation is infrared [and some red] black-body radiation emitted when the universe...
Hello I am studying mechanics and I have been reading about having the reference frame fixed at a certain point, body fixed and also the gyro equations.
I an identify the gyro case easily as I am looking for an AAC body which rotates about an axis.
I am confused about the other two cases in...
Is there a clear reference article/note for the 20X20 Hamiltonian matrix of the spds* Zinc-Blende system similar to the sps* reference in
[1] Table (A) of Vogl P, Hjalmarson HP, Dow JD. A Semi-empirical tight-binding theory of the electronic structure of semiconductors†. J Phys Chem Solids...
Homework Statement:: Please see below.
Relevant Equations:: Please see below.
I am trying to find a reference to a textbook or a paper that details the following time-invariance Kaluza-Klein metric:
\begin{equation}...
Although I am not a physicist, I am interested in physics, and recently I've been reading about special relativity. I have a doubt about it, a difficulty I see in the equivalence of all inertial reference frames which I haven't found solved anywhere, and I've thought perhaps you in this Forum...
I was starting out some problems on force and motion at 10+2 level. I was told you don’t need to know about frame of reference. But I want to. So which books are there to understand frames? Is it a part of relativity? If yes then which books?
Thank you guys.
There are some question involving the statement. One of them is about the charge density in S' frame. It asks to calc it.
I thought that i could calculate the electric field in the referencial frame S' and, then, use the formula
$$ E = \lambda / 2 \pi \epsilon l $$
In that way, i would obtain...
1) Basic python only no data science or machine learning or game development.
2) I have CS experience and some programming experience but I am really bad programmer, so you can discount my programming experience. But I can learn cs concepts on the go.
3) Contains lots of solved and unsolved...
Hi,
Suppose I need to cite some information from a source. I think it'd be easier to explain using an example.
In the text below titled "Example Text", I have added the sentences, "Hall effect encoders are also called magnetic encoders. They are very popular with hobbyists these days and have...
Two clocks with photo detectors are 100 kilometers apart at A and B. On the center of AB axis two light pulses are sent to the clocks , synchronizing them. Then a light signal is sent from A to B. The two stationary observers record the time from event at A to event at B. Is there a one way...
Just want to clarify some concepts.
There seems to be difference between reference frame and coordinate system. See https://en.wikipedia.org/wiki/Frame_of_reference#Definition . A reference frame is something has physical meaning and is related to physical laws, whereas coordinate system...
If I have fluid with area 10 and velocity 10, if the velocity increases to 20 the area will become 5. But if we switch to a reference frame moving at velocity 1 opposite this motion, then it would be 10 and 11 to 5 and 21, violating the continuity equation. What is wrong?
v1 - velocity of the rain with respect to the ground
v2 - velocity of the man with respect to the ground
v3 - velocity of the rain with respect to the man
So, v1 = v3 + v2 is this right ?
So, for the man moving with a velocity v2 with respect to the ground, the rain will have a horizontal...
Say 2 cars are traveling side by side at 10 m/s in some flat, wide open space. Relative to each other they are stationary. Relative to someone on the ground they are both moving at 10 m/s. Now say you're in 1 of the cars and you see the other car accelerate, changing his velocity by 10 m/s in...
Hi,
reading the Landau book 'The Classical theory of Field - vol 2' a doubt arised to me about the definition of synchronous reference system (a.k.a. synchronous coordinate chart).
Consider a generic spacetime endowed with a metric ##g_{ab}## and take the (unique) covariant derivative operator...
Here's what I did so far.
The velocity of the first car is ##v = v_0 +at##
Frame of reference S = the road
Frame of reference S' = the second car
thus, v' is the speed of the first car in the frame of reference S' and v the speed in the frame of reference S.
Here's what make me doubt.
The...
If a train is moving at some constant V with a bed sitting still on top. When the train decelerates at some rate -A then the bed will move at some acceleration A. I can't seem to get an intuition for how this comes to be. I have looked online and find no help.
Studies of the Cosmic Microwave Background shows that the Earth is moving roughly 380 km/s with respect to it towards the constellation Leo I think. Yet (I think) the Cosmological Principle and the Michelson-Morely experiments suggest there is no preferred reference frame in the universe --...
In trying to understand a bit of special relativity, I want to make sure if I understand it correctly, and I came up with the following question: "Imagine you would know all forces in the universe acting upon an object, doesn't that give away the only real existing frame of reference (imagining...
Hi,
I've a doubt about the application of the principle of relativity as follows.
Assume as principle of relativity the following statement: It is impossible by any experiment performed inside a "closed" laboratory to say whether we are moving at constant velocity or staying at rest.
Consider...
Good morning!
I know this may sound a little odd, because there is a theorem regarding it, but i have this question.
Basically, a CFD analysis gives me the value of the forces and the moments, as a function of fuselage's orientation, in a particular frame of reference.
How can i calculate the...
Newton's laws only hold in intertial frames. In general, the center of mass (CM) is accelerating, so it cannot be used as a frame. However,
1. Suppose that CM is accelerating only in the ##\hat{z}## direction. Does this mean that the CM frame is still valid in the ##\hat{x}## and ##\hat{y}##...
Hello Everyone,
I am trying to understand the usefulness of a body-fixed (body-centered) frame of reference ##O'x'y'z'## versus a lab frame of reference ##Oxyz##. The body-fixed frame is attached to the moving body and changes orientation exactly as the body changes orientation. From the...
My youngest is a fabricator for GM, working in their autonomous car division. She's doing so well she just opened a trade school to teach people how to use a five axis milling machine, with her own money no less AND still keeping her day job. (Lord! five axis milling machines cost over a...
2 balls (Ball 1 and Ball 2) collide fully elastically and their relative velocity stays the same as but in sign opposite to that before the collision. Is there any sort of reference frame in which Ball 2 is always fixed (at rest) so that one can look at their relative velocity always in that...
Hi everyone,
I'm curious if anyone knows of a reference book on enzymes that discusses each enzyme's catalytic mechanism(s). I've consulted several books that explain the different categories of enzymatic catalysis but I'm looking more for an encyclopedic reference that explains such...
A very basic and simple query, but I can't see my way through it.
A mass m moves at speed v1 relative to a truck traveling at speed v2 , fig.a. All components except this mass are massless.
In a truck-stationary frame, the mass collides with a barrier on the truck liberating kinetic...
I was trying to look for something that works a lot of examples of integrals over surfaces, volumes etc. in general relativity. Tong's notes and some others are good on the abstract/theoretical side but it'd really be better at this stage to get some practice with concrete examples in order to...
There is a nice fact. It approximately sounds like that: Let ##H=H(p,q)## be a Hamiltonian system with ##n## degrees of freedom such that all its orbits are closed. Then the periods of all the orbits belonging to the same energy level are the same.
Please which textbook does contain this? I...
Hello,
here on PF I've seen many threads about the concepts of 'reference frame' and 'coordinate system'.
In the context of SR my 'envision' about the concept of 'frame of reference' is basically the 'rods & clocks latticework' as introduced in the book Spacetime physics (Taylor, Wheeler)...
I am trying to figure out what are inertial observer and inertial frames of reference. The law of inertia holds for inertial observers. Inertial observers are objects with zero net force acting on them, and move with constant velocity. Suppose we fix a set of coordinate axis in space, relative...
Hello! I am dealing with a problem of a 2 level system (an ion in my case) placed in a Penning trap. Basically the ion is moving inside the trap under the influence of the magnetic and electric field and I need to study its inner 2 level system (basically the lowest 2 energy states) while it is...
This is not a contextual question, but a stylistic one; hence it doesn't seem to belong in the other threads.
I am proof-reading a paper, and I am unsure about the way the author uses square brackets for the indication of (numbered) sources. In order not to be quoting a source without...