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. K

    Find drag given reference area and speed

    Homework Statement What is the drag force on a 1.6 m wide, 1.4 m high car traveling at 30 m/s (approx 65 mph)? Homework Equations drag force=.5*p*v^2*coefficient of drag*A The Attempt at a Solution density of air depends on temp but that's not given so I used a density of 1.2...
  2. W

    Particle energy and momentum in different reference frames

    Homework Statement A particle is observed in a certain reference frame (i.e. observer A) has a total energy of 5GeV and a momentum of 3GeV/c. (a) What is the energy of the frame in which its momentum is equal to 4GeV/c. Homework Equations E'={\gamma}E-{\gamma}{\beta}(cp)...
  3. S

    Frame of Reference: Does Stuff in the Frame Matter?

    Okay, weird question. Sorry if this is really stupid but it's been bugging at me for days now. First, let me lay out my current assumptions/understanding of what's going on. The current theory seems to be (to an amateur like myself) that there is no fixed space-time. That to talk about...
  4. G

    Electromagnetism in Reference Frames

    If observer A was at rest with respect to a charge that was moving with a constant velocity |v| > 0 in observer B's reference frame, would observer A detect a magnetic field?
  5. Jonnyb42

    Speed of light in Non-Inertial reference frame?

    I see a lot of places, "The speed of light is the same in all inertial reference frames." But is it the same in non-inertial reference frames too? For example, your reference frame/observer is accelerating according to someone else holding a flash light, at the moment they meet, the other...
  6. A

    Reference Frames in Simultaneity

    Lets say that a person in a moving train throws a ball in the direction of motion from one end and hits the other end of the train at 10 mph (relative to the person on the train). According to special relativity, from the perspective of a platform observer though they would see the ball having...
  7. J

    Quick Reference Frames Problem. Soon

    A ferry cross a river of width d. The speed of the boat is v relative to the water, and the speed of the tidal current is w parallel to the riverbanks. The ferry landing points are directly opposite each other on each side of the river. How long does the shortest return trip take? My attempt...
  8. A

    Why does Newtonian mechanics include relative motion between inertial frames?

    I know that in Newtonian mechanics an inertial frame of reference moves relative to absolute space. But why does Newtonian mechanics include the contention that two inertial reference frames move relative to each other? It seems that if you have an absolute reference frame then there is no...
  9. M

    Help with frame and reference problem

    You are on an airplane traveling due east at 100 m/s with respect to the air. The air is moving with a speed 35 m/s with respect to the ground at an angle of 30° west of due north. What is the speed of the plane with respect to the ground? __________ So here's what I am doing: Drew the...
  10. P

    Reference book for gravitational force

    hi, please anybody tell reference book for gravitational force, quantum gravity, black holes.
  11. O

    Do Laser Beams from Spacecrafts Travel at Different Speeds?

    Hey guys I don't think i have the correct solution to this question. I would say tht the laser beams would bothe reach the planet at the same time, but this just seems way too easy. Any hints/thoughts/suggestions on solutions to this question? Thanks Two spacecraft are flying towards a...
  12. P

    Hi,please anybody tell any reference book for astrophysics.

    hi, please anybody tell any reference book for astrophysics. i am interested to study celestial body and black hole. where it is available ?
  13. S

    Is there preferred reference frame for motion in the universe.

    For a long time, I have wondered if space has a preferred reference frame. As one looks at the cosmic microwave background radiation, ask your self what would it look like if I accelerated myself in one direction. You would expect a bluer shift in one direction and redder shift in the other...
  14. P

    Relativity, reference frames and Lorentz transformations

    Homework Statement The system S' moves in relation to the system S with velocity \upsilon along the -x- axis. At the time when the beginnings of the coordinate system are in the same point, clocks in both system shows t=t'=0. Which coordinates will have a reference point during the motion in...
  15. A

    How does the energy and time dilation of objects moving at high speeds work?

    Assume you have two objects, with nothing else, moving directly away from one another, each at 51% of the speed of light. But, from the frame of reference of one object, the other is going 102% of c, an impossibility. How does this work? And: Those same two objects, which has more energy...
  16. atomqwerty

    A question about reference system and time dilation

    Hi everyone, These days I've been reading about relativity (special) in a book of general physics, and I have a doubt about the reference system: If I stay on Earth and I observe a rocket traveling away from the Earth with a great velocity (let's be 0.5c), and I notice that time inside the...
  17. E

    Inertial reference frames problem

    Homework Statement An example of an inertial reference frame is: A. any reference frame that is not accelerating B. a frame attached to a particle on which there are no forces C. any reference frame that is at rest D. a reference frame attached to the center of the universe E. a reference...
  18. DaTario

    Experimentally probing the photon's reference frame

    Hi All, Suppose a photon is approaching the origin of set of three cartesian axes, along the negative part of the z axis. If we put a slit, geometrically defined as: 1a) half plane z = 0 and x >= epsilon 2a) half plane z = 0 and x <= -1 * epsilon Note that the slit width is 2 *...
  19. B

    Newtons first law and inertial reference systems. (noob)

    Hi everyone, Recently i started a self-study in classical physics by reading through some books. In the section that described Newton's first law I stumbled upon something that did not make much sense. The following section of text got me confused. "If the net force acting on a body is...
  20. F

    LaTeX Latex Homework Ref: Get Help in Forums

    Homework Statement Can someone point me to a reference for Latex that can be used here in the forums? Thanks.Homework Equations The Attempt at a Solution
  21. D

    De Broglie wavelength and it's dependence of the frame of reference

    Hello, I've always wondered about the "relativity" of the De Broglie wavelength. The wavelength depends on the momentum of the specific thing we are observing, thus on different frames of reference(F.O.R from now on :P) we might get different answers. I have been looking through the web to...
  22. W

    Any good reference on construction of irreducible representations of SU(N)?

    how to construct an irreducible representation of SU(3)?
  23. M

    Rotating reference system - centrifugal force

    Hi! Can someone explain this expression for the centrifugal force? F = -mw x w x r, where the underline refers to vectors. (sorry for notation) w is the angular veolcity, m mass, a r is the radial vector. I can't really see where the expression comes from. Can you indentify and...
  24. E

    Need reference for material properties

    I am an electrical engineer and not familiar with this. I need to look up the permittivity and conductivity, density and acoustic speed of some common fluids: sea water, de-ionized water, castor oil, alchohol, ... Where would I find some reference containing these numbers? Thank you.
  25. F

    Kinetic energy, heat, and reference frame

    I'm having some trouble reconciling the following facts: 1) that kinetic energy depends on v _squared_, 2) at the same time energy is conserved in all reference frames, and 3) reference frames transform linearly in v in classical mechanics (galileo transform). I've basically been able to boil...
  26. B

    Causality violation from FTL signaling within the same reference frame only?

    I apologize if this has been asked before. I searched numerous times and couldn't find any discussion on this specific topic. Every description I've read of the impossibility of FTL signaling uses some variation of this diagram: http://www.theculture.org/rich/sharpblue/archives/000089.html...
  27. W

    Ball dropping and frame of reference

    Consider I am in the train with a ball traveling at normal speed of a train. I drop the ball, it follows a straight path of descent and falls in front of my feet. For an observer on the platform, the ball follows a parabolic path and falls in front of my feet. (Please go to this...
  28. S

    Exploring the Twin Paradox: Searching for the Oldest Frame of Reference

    I was just working on my knowledge of the twin paradox, and had a question that I couldn't find an answer to anywhere: If I understand it correctly the paradox is resolved because the two frames are not symmetrical, one is non-inertial, so that frame has it's clock run slower. So if you carry...
  29. T

    Finding a Natural Frame of Reference on the Cosmic Scale

    I'm looking for a list of "natural" frames of reference on the cosmic scale. Something that can be used as "the" frame of reference for everyone in the universe that isn't arbitrary. So let's brainstorm about some potential candidates. The more the better. If need be, start with an idea and...
  30. T

    How Does Acceleration Affect the Power Required to Overcome Drag?

    I am a bit confused by the equations for Fdrag (the force drag applies to an object) and Pdrag (the power required to overcome drag). F_{drag} = \frac{1}{2} C_{d} \times \rho \times A \times \nu^{2} Where: C_{d} is the Drag Coeffecient (a dimensionless, empirically-derived constant)...
  31. D

    Why is the speed of light independent of a frame of reference?

    I understand the Michelson–Morley experiment and its result; but what I don't know yet is the REASON. Example: A torch in free space is moving at a velocity [v] w.r.t me. Considering the material nature of light, shouldn't the speed of photons emitted from the torch be [v+c] w.r.t ME? According...
  32. J

    Solving Frames of Reference Homework: Static/Kinetic Friction

    Homework Statement A child sits 2m from the centre of a merry-go-round (a rotating wooden platform) which is rotating at 3.5revs/min in a clockwise direction (when viewed from above). She places a wooden block of mass m=0.25kg beside her on the platform. a)Draw a diagram showing all the...
  33. M

    Where Can I Find a Simple Guide to Transformer Design?

    Does anyone know of a good link to basic transformer design? I keep seeing the standard equations but they don't seem like much help. I can't seem to find any good guides for designing the most basic transformer For example, I will see equations relating the ratio of turns to the ratio of...
  34. W

    Any good reference on quantum-classical correspondence?

    after learning quantum mechanics, i tried to abandon all intuitions and pictures in classical mechanics however, it seems that the picture in classical mechanics is often valid and useful still is there any good not so naive reference on the quantum-classical correspondence?
  35. N

    How Is the PDF of the Sample Median Derived?

    I am familiar with the derivation of the probability density function of the sample mean but was looking for an equivalent derivation for the sample median. Does anyone know of a good, clear derivation of this PDF? Thanks, Natski
  36. K

    Observational astrophysics reference for math/physics major

    Hi all, I'm a math major with decent training in physics (through quantum and statmech), and I'd like to learn more about astrophysics. Not so much the theoretical cosmology kind of stuff, though, as how scientists take observational data and deduce things like "the mass of the galaxy" or how...
  37. K

    Understanding Earth's Rotation: Impact on Reference Frames

    Urgent-About reference frames! Hi guy's. I thought about this for quite a while but could not convince myself to believe it. I may be wrong somewhere but still any help would be greatly appreciated. The question: Now the Earth rotates at a speed of 7.29*e^-5 rad/sec.,so that any...
  38. K

    Reference letters: writing the prototype oneself

    Hello Physicsforums, I've been reading here for a while and like this forum a lot. For the following issue I couldn't find a suitable thread so I decided to register and ask my first question: I'm about to apply for grad school, for which I need academic references. I talked to the two...
  39. E

    Point charges in non-inertial reference frames

    Okay, in inertial reference frames, two particles with the same charge will always repel each other. Even if they were moving in parallel at high speeds, and thus producing magnetic fields, special relativity would come in and balance the forces from the electric and magnetic fields so that...
  40. M

    Is black hole existence relative to the reference system?

    Is it possible for a black hole to exist in a reference frame and not exist in another? I did some naive calculations and the result was that what are neutron stars in relation to Earth could be black holes in relation to a proton accelerated near the speed of light at LHC. That is because...
  41. P

    Reference for Summation Formula?

    Hi all, I am desperately looking for a reference for a summation formula, which I have obtained with Mathematica. It reads...
  42. M

    Electromagnetic force on a particle in two different frames of reference

    Consider an infinitely long straight conductor carrying a current. Let's assume that the free charges in the conductor are positive and are moving at a drift velocity v. Now, consider a particle of charge +q also moving with v in the same direction as the current at a distance r from the...
  43. jaketodd

    Does the graviton move at the speed of light in any reference frame?

    Does the graviton move at the speed of light in any reference frame? Thanks, Jake
  44. Z

    If velocity is subjective to an observers frame of reference?

    If velocity is subjective to an observers frame of reference, then isn't energy (kinetic) also subjective? How can we define energy as objective if it changes depending on your frame of reference?
  45. P

    Frame of reference of any observer

    Let's consider flat 4D Minkowski spacetime. Is it possible to define (local) coordinate system for any observer (its natural reference frame) so that these coordinates posses interpretation of time and spatial position measured by this observer? It can be done in two dimensional Minkowski...
  46. B

    Where Can I Find a Comprehensive Chart of Metal Conductivities?

    Does anyone know where I could find a good chart listing the thermal and electrical conductivities of metals? The chart doesn't need to be terribly accurate, I only need to know general values for comparison to other metals on the chart. All I need is one basic value for each metal. If anyone...
  47. J

    3d projectile motion, with rotating reference frame

    Homework Statement I'm using MATLAB show the path of a projectile fired directly up(directly out from the center of the earth) from 41 degrees north latitude. Air resistance, variation of gravity cause by height, and the centrifugal force are for now ignored. What I'm trying to figure out...
  48. B

    Acceleration in an accelerated reference frame? Yes/no/maybe?

    Hi, my question is this, say you’re in a lift that is accelerating downwards at 5ms and you were to drop a 200g wallet from say 1.3m off the floor of the lift, assuming gravity is 9.8ms, how long would it take the wallet to hit the floor of the lift? Does the downwards acceleration of the...
  49. fluidistic

    Calculate Particle Velocity/Accel in Referential w/ Motion & Coriolis Problem

    Problem: Calculate the velocity and acceleration from an inertial reference frame of a particle whose motion functions (in Cartesian's coordinates) are known from a moving referential. The motion of such a referential is in accelerated translation and rotation with respect to the inertial one...
  50. A

    What is the Reference Frame for Rotational Motion?

    we generally study the concept of Inertial reference frame in case of translation motion (for non-accelerated frames) what happen if motion is rotational?
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