Reference Definition and 1000 Threads

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. F

    Frenet-serret formulas, local reference frame

    Hello Forum, Using a fixed, Cartesian reference frame (i.e., we, observers, are stationary and located at the origin of the system), the trajectory of a particle would be easily described by the parametric (parameter time or arch length) equations [x(t), y(t), z(t)] or [x(s),y(s),z(s)]...
  2. 7

    Find Initial Speed of Porsche Using Inelastic Collision

    Homework Statement blah blah blah Homework Equations momentum = momentum' mv + mv = (m1+m2)v (Uk)N = friction force The Attempt at a Solution It's hard to find how to start with randomly given values. Thank you so much for your help! :D
  3. EnumaElish

    U2 song reference to Sci-Fi novel?

    Does anyone think the U2 song "No Line On The Horizon" might be a tribute to Larry Niven's novel Ringworld? The novel describes an engineered, rotating ring-shaped "planet" that occupies an entire orbit around a star. The inside of the ring is populated. Looking afar (e.g. spinward, or...
  4. B

    Frames of reference problem help(grade 12)

    Homework Statement A boat goes at 7.78 m/s [37 degrees west of south] in a current of 2.41 m/s [5 degrees north of west]. Find the velocity compared to the bottom. Homework Equations I think we use this: Vf2 = Vi2 + 2a x delta d The Attempt at a Solution I drew a diagram but...
  5. Y

    Reference Frame Question: How come wind relative to boat doesn't matter?

    Homework Statement http://img198.imageshack.us/img198/3834/relativeboatvelocity.jpg The note says "( Wind relative to boat is irrelevant! )" Why is it irrelevant?
  6. B

    Comprehensive filter design reference?

    In most of the EE textbooks I have, the topic of filter design seems to essentially be treated like "Here are some active filter topologies, and here are their normalized transfer functions, and here are a lot of tables of pole locations for say the 4 pole 1 dB Chebyshev filter. See you later."...
  7. S

    Relative acceleration & reference frames

    Homework Statement 1. You are passing another car on a highway and determine that, relative to you, the car you pass has an acceleration toward the west. However, the driver of the other car is maintaining a constant speed and direction relative to the road. Which of the following statements...
  8. R

    Reference value for magnitude of fft output

    Hi, I'm using a version of daqacquire to acquire a sample of sound data. This program also uses daqdocfft to perform a Fourier transform, allowing me to view the frequencies that are present in my data sample. My problem is that I don't understand how the function is calculating the...
  9. T

    Another 'photon's reference frame' thread

    If we can shoot a photon outward, at velocity c, why is it that the body that shot it outward is not traveling away from the photon with velocity c?
  10. Z

    Understanding Magnetism in Different Reference Frames

    What if i was traveling in a car with an e- with me. W.r.t to a positive charge at rest , it would seem accelerating to me i.e. it would have a magnetic field but acc. to a person on the ground it would just have an electric field. If there were a car moving relative to me , the person would...
  11. G

    A question about special relativity? Car reference vs Earth reference?

    A question about special relativity? Car reference vs Earth reference?? Hi I am prepping for a upcoming exam and I am trying to understand some concepts of physics and special relativity...which my exam will be on and i need to understand these problems so that i can know how to do the rest...
  12. K

    Gravitational Field & Reference Frames

    In Newtonian physics gravity is a force and in relativity it's curved spacetime if I understand it correctly. So my question is, does the gravitational field of an object look different to different observers? What I mean is, does one reference frame see the strength of the field to be greater...
  13. D

    Reference frame for uniform circular motion

    Hi. Say a particle is moving around in uniform circular motion. The way my book attacks this problem is by placing the coordinate system such that one axis is in the radial direction and the other axis is in the tangential direction. Then we have the following for the radial acceleration...
  14. E

    C/C++ Call by Reference in C++: I'm Confused!

    I am confused by two versions of call by reference in C++. As an example two methods that square an integer (CBR stands for Call By Reference): //Version 1 void squareCBR(int& x) { x = x * x; } //Version 2 void squareCBR2(int* x) { (*x) = (*x) * (*x); } Let's call the functions...
  15. L

    String theory and reference frames HELP

    I am reading The Elegant Universe...and I have bumped to possibly the first part of the book that I can not understand. When an electron and a positron pop out of existence, they soon annihilate each other with a "bang"...emitting a photon. If fundamental substance of universe are...
  16. R

    Newton's laws and non inertial frame of reference

    Hi all Why do we actually say that Newton's laws do not hold for non inertial frames. can you folks give me an example of how Newton's laws collapse in an non inertial frame(if they do at all)
  17. D

    Reference area, in drag coefficient formula

    hi small question in the drag coefficient formula for boats and ships, is the reference area, the surface area of the submerged part of the ship/boat? demson
  18. A

    Special Relativity and reference frames

    Here's a statement that I'm supposed to solve: (\Deltax')2 = (\Deltax)2 - c2(\Deltat)2 And the accompanying text: "Show that (the equation above) is the same for all reference frames in special relativity" I consider myself somewhat decent with your basic special relativity calculations...
  19. C

    Good reference book to learn all aspects of causality violation

    Hello everyone. I was wondering if anyone knew any good books of learning the aspects of causality violation in general relativity. I know about Hawking book but that's all. I was wondering if anyone had any references to authors in this area at any level from introductory books that are self...
  20. N

    Can we predict which reference frame is correct?

    I was thinking about something earlier today. One of Einstein's famous phrases is "I can not believe God plays dice with the Universe." After pondering on this for a while, something confused me. Say for example we have a group of observers who all observed the Simultaniety of an event...
  21. W

    Some advice on linear algebra reference book

    I am going through the MIT OCW on Linear Algebra [18.06] by Gilbert Strang. The problems which they have on the site are all references to Gilbert Strang's book on Linear Algebra. I cannot buy the book as of now. However, I have got hold of a copy of a book called Linear Algebra by Hoffmann and...
  22. M

    Oscillating table and reference frames

    Homework Statement A horizontal table oscillates with a displacement A sin ωt , where A = (Ax , 0, Az ) is the amplitude vector and ω the angular frequency in an inertial frame of reference with the z axis vertically upwards, normal to the table. A block sitting on the table has mass m and...
  23. B

    I have some money for some reference books

    so I am finishing my UG course in physics in about a month or so. however, i had a grant that allowed me to buy books for my course. I have about 130 pounds left. im probably going to go into the field of optics hence born and wolf is an often quoted choice (perahps the optical coherence...
  24. V

    Understanding Frames of Reference in Relativity

    Im trying to understand frames of reference, I am very new to relativity so sorry if I am being silly! Suppose you have a 2 spacecraft one traveling relative to the sun, and the other traveling relative to the first spacecraft in a perpendicualar direction. i know the velocitys of...
  25. D

    Reference for photoluminescence data?

    I'm writing a lab report about the photoluminescence of two chemicals, (1) indocyanine green and (2) hexamethylindotricarbocyanine tetrafluoroborate. I've done the experiment, and now I need to (well, I've been advised to) find some data in a published paper or reference book to compare my...
  26. T

    Collisions and changing frame of reference?

    collisions and "changing frame of reference?" Homework Statement A 6.0Kg trolley moving at 6.0 m/s right overtakes and collies with a 2kg trolley moving 2m/s right in the same direction on the same track. The collision is cushioned by a perfectly elastic bumper attached to one of the trolleys...
  27. C

    Special relativity inertial reference frames.

    [b]1. Suppose the space time co-ordinates of two events in inertial frame S are as follows: Event 1: x1=x0, t1=x0/c y1=z1=0 Event 2: x2=2x0, t2= x0/2c y2=z2=0 Show that there exists an inertial frame s' in which these events occur at the same time (i.e t1'=t2') and find the value of time...
  28. T

    How do you tell you are not in inertial frame of reference

    While explaining about inertial and non-inertial frame of reference, people give this example-- http://www.phys.unsw.edu.au/einsteinlight/jw/module1_Inertial.htm if you don't wish to follow the link, here is a simple explanation---> there are two person and a rotating disk. Person A is in...
  29. K

    Reference Material Needed for Essay on Radioactive Decay

    I have an essay on radioactive decay, here is the title 'Explore the nature of radioactive decay and Discuss it's applications' Does anyone know any good reference material for this kind of thing? Equivilence of mass and energy Alpha, Beta, Gamma Nuclear power Med Physics Carbon...
  30. S

    CompSci: Undefined reference to

    Homework Statement I'm compiling ExprTree.cpp and it's giving me an Undefined reference to 'BinaryTree::BinaryTree(std::string)', 'BinaryTree::toString()', 'BinaryTree::~BinaryTree()', and an undefined reference to '_WinMain@16' ExprTree inherits from BinaryTree Homework Equations...
  31. F

    Reference Material for Undergraduate Level Vibrations Courses

    Hello everyone, I am a junior Mechanical engineering student with a midterm in my Vibrations I class on Thursday. I've been studying but I'm having some issues really nailing the concepts fundamentally. I feel like I'm stuck in a rut of doing the problem like in the example, but not really...
  32. Q

    Special relativity - frames of reference

    Homework Statement We have two frames of reference: K (x,y,t) and K' (x',y',t') such that initially x=x'=y=y'=t=t'=0. Now let K' move with a velocity \vec{v} = v [\tfrac{1}{\sqrt{2}},\tfrac{1}{\sqrt{2}}] Write Lorentz transformations in such a case. Homework Equations The Attempt at...
  33. B

    Cosmic microwave background and a reference frame

    Dear Friends A fleet of spaceships is given, each equipped with a differential microwave radiometer, just like COBE was, whose detectors are antipodeanly pointing (this way one should catch blue shifted radiation and the other one red shifted). Could their acquisitions be used to...
  34. P

    Simple Harmonic Motion and Reference Circle

    Thank you in advance! Homework Statement A 3.0-kg block is between two horizontal springs. Neither spring is trained when the block is at the position labeled x=0 m in the drawing. The block is then displaced a distance of 0.070m from the position where x=0m and is released from rest. (a) What...
  35. M

    Lorentz force: absolute reference frame?

    F= q(v x B) B= v x q*k*d/r^2 It is a basic physics knowledge magnetic field forms around moving charge, it tell us magnetic field is zero when charge is not moving and strength of magnetic field increases as velocity increases, right? Magnetic potential vector field increases with "absolute...
  36. G

    Quantum Physics Reference and Direction

    Hi, I am an Electrical and computer engineer. I recently decided to start studying physics in my spare time in the futile attempt to understand the universe, or at least parts and interpretations of it. I decided to start with quantum physics, a book called "Quantum Theory" by David Bohm. It...
  37. C

    Simple Harmonic Motion and the Reference Circle

    Homework Statement A loudspeaker diaphragm is producing a sound for 2.5 s by moving back and forth in simple harmonic motion. The angular frequency of the motion is 7.54 x 10^4 rad/s. How many times does the diaphragm move back and forth? Homework Equations angular freq. (W for...
  38. M

    Deriving acceleration in rotating reference frames

    Hi, everyone:) In my mechanics book a derivation is given for acceleration in rotating reference frames. However, there is one step I don't understand. First of all, it is derived that v=v'+\omega\times r' or \left( \frac{dr}{dt}\right) _{fixed}=\left( \frac{dr'}{dt}\right) _{rot}+\omega\times...
  39. J

    Frames of Reference: Exploring Motion & Inertial Frames

    I keep hearing how motion only exists relative to something else. But what if there is some object in space, and it is the only object in the universe. It has some kind of propulsion system, and it activates it, goes to a certain speed, then stops accelerating. Is that object really moving, or...
  40. B

    What Happens to Time if a Clock is Independent of its Reference Body's Motion?

    Einstein wrote ... Q: What would happen inre (in regards to) time if, for any reason, a clock were to be 'independent of the state of motion of [its] body of reference'? A: _____ (?)
  41. S

    What is absolute reference pressure and absolute reference temperature

    What is "absolute reference pressure and absolute reference temperature" I am doinf a test about compressed air flow rate. There is a parameter called absolute reference pressure and absolute reference temperature. Are they 1.01bar and 273+20K?
  42. B

    Reference Books for Embedded & Hardware Design

    I would appreciate it if anyone could add good quality reference books that would benefit me. I graduated in May and I have forgotten a lot of the material especially hardware design wise and my job is a mixture of embedded design and hardware design. The embedded side I am doing fine but...
  43. A

    Spinning Frame of Reference: Inertial or Non-Inertial?

    Homework Statement Is a spinning frame of reference an inertial frame of reference? Homework Equations net torque, net force = ma, equilibrium --> net force = 0, net torque = 0 I've learned that an inertial frame of reference is a frame of reference which is not accelerating. The...
  44. U

    Is a reference frame fixed to a photon an Inertial Frame?

    Hi All, I am a bit confused about reference frames and inertial frames. According to the first postulate of special relativity (if I'm right), all physical laws take their simplest form in an inertial frame, and there exist multiple inertial frames interrelated by uniform translation...
  45. L

    Find the Perfect Physics Reference for SAT Subject Test

    Hi, I am looking for a all-time reference physics book, which will cover the SAT Physics Subject Test. I want a book that will give me a general understanding of Physics(Mechanics, Electricity and Magnetism, Waves and Optics, heat and Thermodynamics, Modern Physics, etc.) Thanks for your...
  46. C

    Universal Reference Point question

    If in the future humans master time travel, might it be valuable to know a Universal Reference point that is common to both the present and past coordinates in space and time. For example, say we designated a single point on Earth from which all other relativistic effects are to be measured...
  47. A

    What is an inertial frame of reference?

    Homework Statement What is an inertial frame of reference? Homework Equations -A particle at rest or moving at a constant velocity in an inertial frame of reference implies that the sum of the forces acting on the particle is zero -The tendency of a body to keep moving once it is set in...
  48. C

    Gravitation (Preliminary Reference Earth Model)

    Homework Statement Assuming that we know the density of Earth as a function of radius, we have to derive the equation for gravity as the function of radius. Homework Equations The Attempt at a Solution lets us choose density as \rho(r). I know that within a hollow sphere there is no gravity...
  49. B

    Inertial Reference Frames and Newtons laws

    Homework Statement I am a bit confused about what are inertial reference frames and what is not. The text states: "We define an inertial reference frame as a reference frame in which Newton's laws are valid... Accelerating reference frames are not inertial reference frames...
  50. P

    Special Relativity and Reference Frames

    Hi, I am a bit confused about a certain aspect of Special Relativity and I am hoping someone can clear this up for me. Let's say we have an event and two observers. Observer A stands a few meters from the event, Observer B is hundreds of thousands of miles from it. Relative to the event and...
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