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.

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  1. B

    Acceleration in a non inertial reference frame

    Homework Statement A platform rotates with ##\omega=10## rad/s around ##z##-axes. A ball is connected, with a yarn to ##z##. Its distance to the axes is 15 cm and it rotates with ##\omega=10## rad/s. There isn't friction between platform and ball. Suddenly, the angular velocity of the...
  2. B

    Prob/Stats Seeking a good introductory book in probability theory?

    Dear Physics Forum personnel, I would like to seek your recommendation on a good, introductory textbook in the probability theory (non measure-theoretic treatment) that contains both the applied and theoretical treatment of the subject. My goal is to advance into the measure-theoretic...
  3. F

    Frame of Reference: Definition & Explanation

    Hello, My understanding is that a a frame of reference is a theoretical framework that is used to describe the motion of an object allowing for measurements of position, distance and time. A frame of reference always implicitly includes a coordinate system (cartesian, spherical, cylindrical...
  4. S

    Submitting an additional reference letter

    Hi, I've submitted my graduate application for some competitive programs and have had all my reference letters submitted. The deadline is now officially gone. However, I have not had my thesis advisor submit a letter of reference. I've talked to some of the programs and they have sent an...
  5. P

    Inertial Frame of Reference vs Spacetime

    Is the inertial frame of reference the same thing as space time?
  6. H

    Changing the frame of reference

    I'm currently doing a student project at uni and I'm trying to design magnetorquers for cubesats.Before I make the prototype I need a simulation of what will happen.The problem is that for my calculations,I need to change the frame of reference of the geomagnetic field.So basically I need to go...
  7. REVIANNA

    Momentum in centre of mass reference frame

    my book says " the total momentum is zero in the centre of mass reference frame.This should not surprise you" but ITS NOT INTUITIVE FOR ME. I am considering a completely elastic collision. 1. I know the v_cm is const because there are no ext forces on the system of the two masses undergoing 1D...
  8. G

    Reference book for ADM formalism

    Hi there, I'm currently looking for a book on ADM formalism in General Relativity. I know that it's definitely not a method really taught so wouldn't be in many textbooks, but was wondering if anyone knew of any great books to use! Thanks in advance
  9. UncertaintyAjay

    Magnetic Force and Frame of Reference

    So, a friend asked me this question in school and I've come up with an answer, I'm just not sure that it is right. Say you have a charged particle moving perpendicular to a magnetic field. There will be a force acting on it given by F=qvB. Now suppose your'e moving along at the same velocity as...
  10. J

    Singularity Theorems: An Accessible Reference

    I've read Hawking's introduction: http://arxiv.org/abs/hep-th/9409195v1, which are nice. I would like something that explains the other singularity theorems and how they are related to Big Bang. I've tried reading Hawking & Ellis but I can't understand most of the definitions.
  11. S

    Reference letter related email etiquette

    I've applied to a particular university for fall 2016 graduate admission. The deadline for my referees to submit the application is December 01. One of my referees is currently extremely busy and has asked me to request the graduate administrator to contact him regarding the reference letter...
  12. T

    Non-arbitrary frame of reference for acceleration?

    The reason we can choose a frame of reference arbitrarily is that a physical system is not dependent on an absolute position, orientation or time. According to Noether's Theorem, the invariance of a system under a change of position is equivalent to the momentum conservation law. In the same...
  13. B

    Time Dilation: Rel. Ref. Frames and Universal Reference Frame

    I understand that if someone is traveling away from Earth at a very high speed, time will slow down for the traveler relative to the people on earth. However, why is it not the other way around? If there is no universal reference frame, could this situation not also be thought of as the traveler...
  14. sandyforever

    Is force independent of reference frame?

    Homework Statement Recently, I have been wondering whether forces are independent of reference frames(inertial and non inertial). From Newton's law we know that the second law is valid only for inertial frames. But what about the non inertial frames. Let ∑F be the net force on an object in an...
  15. sweet springs

    Uniformly accelerating frame of reference

    In an inertial frame of reference let numerous standard rockets that load synchronized standard clocks place on all the space lattice. Simultaneously the rockets start to move with same intrinsic acceleration to the same direction. In other words there exists a common instantaneous inertial...
  16. J

    Looking for book on ZFC axiomatic set theory (I think)

    I am looking for a book that starts at the standard ZFC axioms and progresses to the point where some recognisable non-trivial mathematical statement is proved. By recognisable I mean something that you may encounter in school/early university level and is not purely set-theoretical (e.g...
  17. L

    Reference Data Requirements: What Do I Need?”

    I am requarid to submit reference letter with complite reference data (of my recomendator) could you tell me what dose reference data means? Is it just list of publications of something else? o_O
  18. Raymond Potvin

    B On light clocks and reference frames

    I had this questioning about the light clock on another thread, and DaleSpam suggested that I open my own thread, so here it is. I was asking if the light clock mind experiment was not contradicting the reference frame principle. I added that to my drawings: And DaleSpam answered this: So...
  19. V

    Determining Position and Center of Mass using Reference Frame

    Homework Statement Homework Equations Xcm = (x1m1+x2m2) / (m1+m2) The Attempt at a Solution ok so I'm having trouble understanding what's happening in the question... when the penguin moves, is the sled also moving? If it's friction less ice then if the penguins moves L, the sled will...
  20. E

    EM Wave creation in different frames of reference

    OK, I'm sure I'm just not thinking about this the right way, so please point out my simple mistake. Imagine a charged particle and 2 observers. Observer S is stationary relative to the charged particle, so sees no magnetic field from it. Observer A moves back and forth in front of the...
  21. F

    Using Light as a absolute frame of reference?

    If light travels in a straight line , why can't we use it as absolute frame of reference? This thought experiment is done in the absence of external forces and gravity. One person standing inside a box ,sends a photon parallel to the bottom of the box from one end to another end , whether...
  22. 0

    Invariance of Acceleration in Inertial Reference Frames

    Claim: The acceleration (both direction and magnitude) for any object is the same in any inertial reference frame. Is this claim true? I think it is, but someone mentioned to me that time may be an issue as it's not agreed upon in all inertial reference frames. I'd appreciate any references...
  23. SuperDaniel

    Classical Thermodynamics Tables for Reference

    Does anyone know of a thermodynamics tables for reference to recommend me?... It would be preferable in metric system or in both, british and metric. I searched in the past posts and, I didn't find information about this issue. I found this tables on Amazon, but I prefer to hear from your...
  24. W

    Time Dilation & Acceleration: Leaving Earth Effects

    Leaving Earth at constant acceleration will make time on board go slower. Acceleration will take the ship closer and closer to c Question is: How long will acceleration act on the ship? The time as measured on Earth or on the ship? The final v will be greatly different. Of course, given enough...
  25. D

    Simultaneity: disagreement, in the same reference frame

    Hello PF. There are two lightning flashes , and two stationary observers. Observer 1 who is equidistant from the flashes, sees them as simultaneous Observer 2 stands one step to the side of observer 1, and is not equidistant. He sees the flashes as separate, the light having unequal distances...
  26. Soumalya

    Engineering A choice for a Heat and Mass Transfer Reference TextBook

    Which of the two books would you pick as an undergraduate engineering student if you were to study the subject of Heat and Mass Transfer entirely on your own? 1. Heat and Mass Transfer: Fundamentals and Applications by Cengel & Ghajar 2. Fundamentals of Heat and Mass Transfer by...
  27. E

    Frame of reference: grade 2n vs. grade 2n-1

    Hello all, was it ever a point of discussion in cosmology, quantum-theory, mechanics, etc. that there is a fundamental difference in describing a physical process in a 2n-grade (4th, 6th, 8th-grade) frame of reference in comparison to a 2n-1-grade (3rd, 5th, 7th-grade) frame ? Thanks in...
  28. J

    What's the reference frame for the universe as a whole?

    I'm just beginning physics and teaching myself classical physics from an intro physics textbook and in the 2nd chapter it described reference frames. This got me thinking. My reference frame is the earth, as that is what I use to describe position, displacement, ect. But what is the reference...
  29. notsoclever

    Frames of reference and vectors problem

    Homework Statement A car is moving toward north with a speed of 35 km/h. A truck travels toward west with a speed of 42 km/h. Which is the speed of the caravan according to the car's driver? Homework EquationsThe Attempt at a Solution The solution given by the book is 15 m/s with direction...
  30. E

    Classical mechanics - hunter and monkey - frame of reference

    Hi, This might sound very basic and but i am just starting to learn physics. I an lecture by prof. walter lewin, he descibes the hunter and monkey scenario. The monkey jumps from the tree as soon as the hunter aims and shoot his gun. the bullet hits the monkey anyway. In calculating the time it...
  31. Handsome jack

    Solving the Mystery: Plane of Reference Question

    I saw random question somewhere on the internet a couple of weeks ago and it got me really thinking about it. Supposedly you got a remote control miniature toy helicopter hovering inside a bullet train, if the bullet train suddenly started and accelerated to 200km/hr in 3.5 sec, will the toy...
  32. F

    Torque on a fixed reference of falling masses

    I had a little thought experiment, in which there are two objects with the same masses near each other (same height) on freefall. If I set up a point that is on an instant besides the two masses and call it the center of torque, I get that the torque produced by the nearest one's weight is...
  33. thegreengineer

    Nodal analysis, choosing reference node confusion

    I know that when we have to identify the nodes for solving a circuit with nodal analysis we always have to designate a reference node (which will be the ground node) as a reference for measuring the others' voltages. However I was practicing this and I found this example on...
  34. T

    Reference wanted: surface and interface

    I am a Ph.D. student just beginning my research. Recently, I found several papers about surface and interface interesting, so I want to know more about this area. However, I cannot find any specific review which can give me an overview of this area. Can anyone give me a link to such literature?
  35. SuperDaniel

    Interesting pocket reference by Thomas Glover

    I know that most of you have grown up in this digital era, but me myself, I am a old school man, and, I usually use reference books. Today, I would like to recommend a small and practical book. Have you ever been working in an installation, in the middle of the Amazonian jungle or in the...
  36. EJC

    Schools Who Should I Ask for Letters of Reference for Grad School

    I'm applying to grad schools and my undergrad has a very small Physics department - only 3 professors. I am having at least 2 of them write me letters of reference, but in regards to my third letter, should I ask the other professor, who I've only had a few classes with, or should I ask my...
  37. M

    Accepted without reference letter

    Hello, I will be applying to universities in England for fall 2016 entry and I have one particular concern. I have studied independently instead of attending an ordinary high school, but I've taken and will be taking various exams. Because of this I have no one who can write a reference letter...
  38. pixel

    Properties of light in 2 moving reference frames

    In the usual derivation of time dilation in special relativity, we have two frames of reference, A and B, moving relative to each other with velocity v. In A's frame, a light beam is directed vertically upward toward a mirror and reflected vertically back down. In B's frame, the light follows a...
  39. A

    Lorentz force in different frames of reference

    Hi, I have been studying lorentz force . The book says force experienced by a charge in magnetic field is But velocity is a relative concept . In one frame of reference(inertial frame) I might observe the charge moving with some velocity and in the 2nd frame(inertial too) I might observe the...
  40. a1call

    Frame of Reference Dependant Mass & the Resulting Conflicts

    Hello, Please: • Assume a universe void of all matter • Visualize 2 parallel paths, 10 meters apart. Let’s call them x and x' • Vessel X is moving along x and vessel X' is moving along x' • Vessel X has a mass of 1 metric ton and vessel X’ has a mass of 2 metric tons • At t0 the...
  41. G

    From RTN reference frame to ECI and orbital elements

    Hi all, I'm curently meeting the following problem and can't figure it out by myself. Assume we have to vehicles in space, a target and a chaser spacecraft . The target spacecraft defines the RTN frame of reference. Given the position and velocity of the chaser in RTN-coordinates, how can I...
  42. Natasha Rivol

    Discover the Top Physics Reference Book for Foundation Science Students

    Hello. Can i know which reference book is the best for physics? I am a foundation in science student
  43. Tonia

    Show that Newton's 2nd Law is *Not* valid in a reference frame

    Homework Statement Show that Newton's Second Law is NOT valid in a reference frame moving past the laboratory frame of problem 1 with a constant acceleration? Problem 1: In a laboratory frame of reference, an observer notes that Newton's Second Law is valid. Show that it is also valid for an...
  44. Tonia

    Show that Newton's 2nd Law is Not valid in accelerating reference frame

    Homework Statement Show that Newton's Second Law is NOT valid in a reference frame moving past the laboratory frame of problem 1 with a constant acceleration? Problem 1: In a laboratory frame of reference, an observer notes that Newton's Second Law is valid. Show that it is also valid for an...
  45. Alpha123

    What is the velocity of particle x with reference to Y?

    Homework Statement Particle X moves with a velocity of 15 m/s[R]. Particle Y moves with a velocity of 5.0 m/s[L]. What is the velocity of particle X with reference to particle Y? The correct answer is 20 m/s (R). I do not understand what velocity in reference to particle Y means, and how to...
  46. U

    Why ISO-OSI model is considered as a reference model?

    Why ISO-OSI model is considered as a reference model?
  47. M

    Reference Request - Books for mastering Data Structures

    Thank you for taking the time to stop by this thread. I am in a Computer Science Engineering course and have just finished my first year. I don't think the first year was very fulfilling in terms of quench in my thirst for knowledge. But that's alright because it was largely unrelated to my...
  48. Tonia

    Show that Momentum is conserved in a reference frame

    Homework Statement https://answers.yahoo.com/question/index?qid=20150607101609AAs8C9t Show that momentum is conserved in a reference frame moving at 10.0 m/s in the direction of the moving car. Homework Equations Mass M for 2000 kg car, Mass m for 1500 kg car. To the observer on the ground...
  49. Mysteryciel

    Kinetic Energy and Reference Frame

    I know that kinetic energy depends referance frame is there any article about this issue thanks ?
  50. Mysteryciel

    Can the CMB Reference Frame be Changed in the Newtonian Friedmann Equation?

    I know that in physics we can change referance frame.The Newtonian Friedmann equation is ##H^2-{8πGp /3}={-k/a^2}## I know that this equation derived from CMB referance frame.Now can we change this referance frame ? (And If you can give me an article about this issue I will be very happy,I...
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