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. B

    Best quantum mechanics text for reference in condensed matter theory

    Hi everyone, I would like to ask if anyone can recommend a quantum mechanics textbook as reference for a condensed matter theorist. I am reading a book that requires material I do not remember seeing in my (voluminous) grad QM text (Shankar). It seems to me all quantum textbooks have their...
  2. C

    How Do Voltage Arrows Indicate Polarity?

    I see a lot of voltage drops being represented as an arrow. Say a voltage of 20V is represented as an arrow from point a to point b. What is the polarity of and b then? Do the arrows to represent voltage usually go from + to - or from - to +? Thanks for your time.
  3. C

    Current reference direction confusion

    Homework Statement I have two questions. 1) The ends of a length of wire are labeled a and b. If the current i from a to b is negative, are electrons moving toward a or b? 2) We have a circuit element with terminals a and b. The voltage and current from a to b are both positive. If...
  4. B

    Transforming momentum between inertial reference frames

    Homework Statement A bug of inertia m_B collides with the windshield of a Mack truck of inertia m_T \gg m_B at an instant when the relative velocity of the two is \boldsymbol v_{BT}. (a) Express the system momentum in the truck’s reference frame, then transform that expression to the bug’s...
  5. C

    Time dilation, reference frames

    Hi, Basic question. I'm confused by a time dilation example (37.3 in Young and Freedman 11th ed.). Mavis is moving at .600c relative to earth-bound Stanley, and at the instant she passes, both start timers. Part b asks "At the instant when Mavis reads .400 s on her timer, what does Stanley...
  6. R

    Where is the intertial frame of reference applicable?

    (Please forgive me for the obvious stupidity of this question) I'm trying to understand Newton's laws down to the last detail, because that is how I study things. However, where would the principle of inertia ever take place? And since Newton's laws are only applicable in an inertia frame...
  7. J

    Frames of reference, trajectory

    I'm hoping you can help with a debate I'm having with a friend regarding whether throwing a ball in a headwind is the same or different from throwing a ball from a moving platform (lets say an open boat). If you want some numbers, could you please work with these: For the static throw, can...
  8. I

    Frame of reference - forces in a turn (airplane)

    Hi, I've seen the forces in a turn depicted two different ways: http://selair.selkirk.ca/Training/Aerodynamics/images/lf-turn.gif http://www.free-online-private-pilot-ground-school.com/images/forces_during_turn.gif Which one is correct? I think the first one would be since it's...
  9. C

    Reference frames, reference particles, coordinate systems and all that

    Previously, before getting into relativity, I've always thought of a 'reference frame' of basically an "observer carrying a coordinate system" - where I thought of an observer as anything which could record information of positions and velocities of particles etc. Now, however, I'm reading a...
  10. I

    Thomas Precession, Angular Momentum, and Rotating Reference Frames

    If any of you have the Third Edition of Classical Electrodynamics by John David Jackson, turn to section 11.8, as that's where I'm getting all this from. If not, you should still be able to follow along. In said section, Jackson gives us this equation that relates any physical vector G in a...
  11. G

    Which Textbooks Are Best for Biochemistry Majors?

    Hi there, I found this site while looking for the "best" textbooks in various disciplines. I am majoring in biochemistry, but I rarely buy textbooks. I usually download (torrent) them because I am unsure of their quality and reputation, and I am also usually quite broke. However, I do want...
  12. L

    Reference materials to understand methods of solar-powered cooling

    I am working on a concentrated solar heater using a linear fresnel reflector. I want to learn how I can harness this heat to power a cooling system, preferably with minimal use of electricity. I am in India, so this has a huge ground for application. I was looking at ideas here, and while...
  13. H

    Good reference book or links for material selection

    Hi Everyone, I am basically a post graduate student try to set up my own business. Its a mechanical based business. I come across activities like material selection, fabrication, machining & installation and commissioning. In short turnkey projects. Since my activities are customer based...
  14. K

    Simultaneous events in different frames of reference

    Homework Statement In frame F there are two lights on the x-axis at D and -D (D=0.6x10^9 m ) which flash simultaneously when t=0. There is another frame F' which moves at v=0.8c in standard configuration with F. I need to work out when observers standing at the origin of both frame F and F'...
  15. J

    Rotational Kinetic Energy of Body in another body reference frame

    I have two rigid bodies floating in space that are kinematically constrained by a joint (think of a 2 dof link mechanism floating in space). I have a body fixed reference frame on each rigid body plus the global space-fixed reference frame. The first rigid body is in the space-fixed...
  16. M

    Is an Accelerating Reference Frame Valid for Line Follower Robot Calculations?

    I'm attempting to build a line follower robot and I'm currently in the process of building appropriate models. For the control system I need to define a coordinate system. The most convinient coordinate system from many point of views would be a coordinate system that moves along and changes...
  17. D

    Understanding Reference Frames for Observing Real-Time Events

    What is the criteria to see the latest state of some object which exists after all the previous states in other reference frames? For instance, one observer may see a plane coming off the airport as 'present', other may see 'its flying' as present, but what is the criteria of those reference...
  18. B

    Exploring the Mystery of Earth-Centered Time Reference

    Haefele and Keating flew an atomic clock from the west coast to the east coast in 1971 and then they flew it back. The east going clock lost 59 +- 10 ns and the west going clock gained 273 +- 7 ns. What I do not understand is why they used the center of the Earth as a reference frame, and not...
  19. J

    Confused about the Equivalence Principle and Inertial Reference Frames

    Hey everyone, I started reading up on GR a couple of days ago, and I'm somewhat stuck on the concept of a free-falling IRF. I understand that an observer on a free-falling small spaceship would experience the laws of physics in a rather simple form, eliminating the need for a force of gravity...
  20. S

    Preparing for the GRE: Math & Physics Reference Books

    Dear folks, I decided to prepare myself for taking the GRE on mathematics and physics next year, and coming from a non-traditional path (undergrad in music, basically self-taught in scientific matters), I'd like to ask you about some reference books and, thus, about the actual level of each...
  21. H

    What Are Some Recommended References for Luminescence Spectroscopy?

    I've been looking for a good reference for luminescence spectroscopy but I haven't found anything. Could anyone please help me?
  22. X

    Physics frame of reference, is this possible?

    Homework Statement Generic collision question. For example, let's say you are asked the following question: Object 1 is 10kg and is traveling at 10 m/s [right] Object 2 is 5kg and is traveling at 2 m/s [right] Find their final collisions after impact Homework Equations m1v1 +...
  23. S

    Frictionless ball in a rotating reference frame.

    Homework Statement Imagine that a circular disc is rotating with a frictionless ball on it( ball is not at center of the disc) If we observe the motion of the ball from the rotating frame of reference, then how can we describe its motion? Homework Equations The Attempt at a...
  24. Sneakatone

    Find final velocities in the reference frame to the ground.

    for the 1st two I used v is to the reference frame = 37m/s- -35m/s=72m/s a)ball=[(m2-m1)/(m1+m2)]v bat=v2=[(2m1)/(m1+m2)]*v b) I do not know how to solve for part b. The Attempt at a Solution
  25. D

    Is the earth in a non-inertial reference frame?

    So I would agree that it has a uniform tangential velocity but would the centripetal acceleration of the Earth put it in a non inertial frame.
  26. B

    Fictitious forces in rotating frames of reference

    I got stuck going over the derivation of fictitious forces in rotating frames. see specifically http://en.wikipedia.org/wiki/Rotating_reference_frame#Time_derivatives_in_the_two_frames this page to see the proof I'm talking about (sorry i'd love to be able to explain it by myself but...
  27. O

    Can an Electron Be a Frame of Reference in Quantum Mechanics?

    How does the concept of frame of reference apply to quantum mechanics? Classically something can be a frame of reference as long as it is not accelerating. I often picture in my head an atom with the nucleus fixed and the electron cloud surrounding it. Would it be possible to describe an atom...
  28. A

    Changing the Hamiltonian to a new frame of reference

    Suppose I'm considering particles of mass \mu_i, 1 \leq i \leq 3, located at positions r_i. Suppose I ignore the potential between \mu_1 and \mu_2. Then the Hamiltonian I'd write down would be H = -\frac{1}{2\mu_1}\Delta_1 -\frac{1}{2\mu_2}\Delta_2 - \frac{1}{2\mu_3}\Delta_3 + V_1(r_3 -...
  29. V

    Questions about accelerated frames of reference

    Suppose we have two frames of reference, with one being accelerated (not inertial). This could be you standing on the platform of a train station as a train in front of you is starting. From the train's point of view, you are accelerating, but one obviously knows that it is actually the train...
  30. C

    Time in the reference frame of the photon and aswell curved spac

    Time in the "reference frame" of the photon and as well curved spac Hi there! I understand the tendency of physicists to stick to the math, and the logic itself, and to often avoid attempting to conceptualize a process or law, but that's kinda the opposite of what I'd like to do here. I...
  31. B

    Reference Frames: Understanding Elevator Motion

    someone please help me out with this question: You are in an elelvator that is able to travel up and down a mineshaft. a load is hung from the ceiling inside the elevator on a massless string. You find that the tension in the rope is 10% less than that of the weight force of the load. what...
  32. E

    Point of reference in relative time

    Hi everyone. I rediscovered a question I caught in High-school that I never encountered a answer to. Given a spaceship going back and forth into space, during it's travel it accelerate close to c relative to earth. At an appropriate distance it breaks and returns in a similar fashion. My...
  33. Mordred

    Black hole accretion disk/jet reference

    I found this extremely handy reference on Black hole calculations and models to measure black hole accretion disk/jets. The article also covers several types of BH non rotating and rotating. Methodologies that can be used to distinquish between Neutron and black hole event horizons...
  34. coktail

    Length contraction of space with multiple reference frames

    My understanding is that as I move, from my FoR all objects and space itself (according to Einstein) contract along the direction of my movement. This length contraction occurs for all space and objects in front of me for an infinite distance. Furthermore, relative motion is relative, and the...
  35. N

    Reference Input for State Space Controller

    In the design of a State Space controller using state feedback the input to the plant is given as (where y=x & D=0): u=-Kx If there is a "reference input" then it would be: u=-Kx+r So the state feedback without the reference input simply drives all of the state variables to zero. When there is...
  36. S

    Electric potential reference points confusion

    Hi gang, I am hoping you can clear something up for me. When evaluating the potential of a solid sphere, I find myself confused about the volumes used such that, \phi = Q \int_{\infty}^R \frac{1}{V_1} r^2 \sin(\theta) \, dr \, d\theta \, d\phi + Q \int_R^r \frac{1}{V_2} r^2 \sin(\theta) \...
  37. SredniVashtar

    Is there a Stuff -> Materials it's made of reference around?

    Is there a "Stuff -> Materials it's made of" reference around? This is somewhat a borderline question, but I guess the Materials subsection of the forum is the best place for it. Yesterday I broached a bottle of wine, one with bubbles (that's the most elaborate description my wine expertise...
  38. C

    Accelerated reference frames equation derivation question

    my question comes from the portion of the derivation regarding evaluating the rate of change of the principle axis vectors. this begins by supposing a vector, Q, is rotating about axis n by δθ. Specifically, my question is how from step 4 to step 5 the approximation becomes an equality. Q'...
  39. C

    Accelerated reference frames equation derivation question

    My question regards how the approximation becomes an equality.
  40. W

    Change frame of reference to simplify acceleration calculation?

    I'm working problem from the upper division classical mechanics course on MIT OCW. No solutions are available. This is form the first P-set, question 4. Homework Statement A particle moves in a two dimensional orbit defined by x = A(2αt-sin(αt)) y = A(1-cos(αt)) Find the tangential...
  41. E

    No privileged frame of reference

    As I understand it, Einstein's dismissal of the "luminiferous aether" was based on his discovery that there is no universal frame of reference, i.e. that no frame of reference is privileged in relation to all other frames. My question is whether this principle can also be stated in the inverse...
  42. L

    Is the kinetic energy of an electron the same in all frames reference?

    Homework Statement Is the kinetic energy of an electron the same in all frames of reference? Homework Equations I think that the kinetic energy of an electron is E = hc / λ. However, I am not sure: I got this from searching Google rather than learning it myself. The Attempt at a...
  43. A

    Inertial Reference Frame Locally

    Why can we not CHOOSE a reference frame locally and treat everything inside of it as an inertial reference frame. For example in a classroom, the classroom is moving with the Earth and so is a ball rolling down the class. Because they are both equally moving due to the Earth's rotation, why...
  44. B

    Frame of reference question about equivalence principle

    I've been giving some thought to the new scientist article about the equivalence principle. What initially seems like a very simple issue is remarkably tantalising. (please note- I'm not a physicist so this may be quite stupid) This led me on a little to the question of gravity and direction...
  45. C

    Peskin & Schroeder QFT Born Approximation reference.

    I'm currently teaching myself some QFT trough Peskin and Schroeders Introduction to QFT and I've noticed that in several arguments they rely on appealing to the Born approximation of non-relativistic QM scattering theory. For example on page 121 equation (4.125) they appeal to the scattering...
  46. Y

    Frames of reference for speed?

    So sense speed is relative, could I observe something traveling faster than light? Like in a car, when I see oncoming traffic it appears much faster, so could I not be traveling at, say 1/2c and observe somebody approaching at 1/2c therefore moving at 1c relative to me?
  47. T

    Does light have a frame of reference?

    I know that you're going to probably say that a frame of reference doesn't make sense for light, but I've uploaded a discussion (warning: has profanity) from another website (reddit.com) and I'm curious to see if the user Imhtpsnvsbl makes a valid point.
  48. A

    Three-Body orbital simulation reference plane

    Hello, I have a little three-body (well n-body but let's just worry about 3 now) simulator. I input six Keplerian orbital elements (period P, eccentricity E, inclination I, longitude of the ascending node W, argument of periapse w and initial true anomaly f). They then get converted to...
  49. S

    Special Relativity with Three reference frames

    Homework Statement In the laboratory frame, event 1 occurs at x = 0 light-years, t = 0 years. Event 2 occurs at x = 6 light-years, t = 10 years. In all rocket frames, event 1 also occurs at the position 0 light-years and the time 0 years. The y- and z- coordinates of both events are zero in...
  50. P

    Reference frame to calculate centroids

    Hi. I was recently calculating some centroids and I was wondering if the point were I choose my origin affects the centroid position. I.e., if I choose my origin at a massive particle, will the centroid be the same as with any other reference frame? Thansk :)
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