What is Reference frame: Definition and 229 Discussions

In physics, a frame of reference (or reference frame) consists of an abstract coordinate system and the set of physical reference points that uniquely fix (locate and orient) the coordinate system and standardize measurements within that frame.
For n dimensions, n + 1 reference points are sufficient to fully define a reference frame. Using rectangular (Cartesian) coordinates, a reference frame may be defined with a reference point at the origin and a reference point at one unit distance along each of the n coordinate axes.
In Einsteinian relativity, reference frames are used to specify the relationship between a moving observer and the phenomenon or phenomena under observation. In this context, the phrase often becomes "observational frame of reference" (or "observational reference frame"), which implies that the observer is at rest in the frame, although not necessarily located at its origin. A relativistic reference frame includes (or implies) the coordinate time, which does not equate across different frames moving relatively to each other. The situation thus differs from Galilean relativity, where all possible coordinate times are essentially equivalent.

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  1. G

    Motion in a Rotating Reference Frame

    Homework Statement A particle moves in a rotating reference frame along the x-axis as x(t) = xo eat (xo and a are positive constants). The frame rotates with a time-dependant angular frequency ω(t) about the x-axis. The true physical force is in the x-direction of the rotating frame. Break up...
  2. K

    What is the reference frame the earth rotates relative to?

    Please excuse my ignorance - I am a biologist by training - but this is one of those questions that just keeps bothering me and I can't find the answer with Google/Wikipedia. Take as our example the ocean currents on the Earth caused by the Coriolis Effect of the Earth turning. When I read up...
  3. C

    Travel faster than speed of light. According to what reference frame?

    I have been reading Einsteins Relativity and a simple concept in special relativity is tripping me up. I have heard that an object can never reach the speed of light. To which observer is this speed limit seen by. I know your answer will be "By all observers" but that is what I don't get...
  4. E

    Universe Age: Exploring the Reference Frame & Relativity

    The experts say the age of the universe is known with considerable accuracy. What frame of reference are they using and why doesn't it violate the idea of relativity to claim to have a preferred frame?
  5. Rasalhague

    Momentarily Comoving Reference Frame

    - http://www.physicsinsights.org/glossary.html I'm often unsure whether people are using "frame" to mean a chart, or a basis field of tangent vectors, or a basis for an individual tangent space. Have I got this (more or less) right? (1) A MCRF of a pointlike object is a function that...
  6. P

    Is there really an absolute reference frame?

    Is there really an absolute reference frame?? According to mechanics as we understand today, all reference frames are equally valid in analysing in the universe, whether measurements are taken relative to the earth/sun... However if all reference frames are equal, why can't we take...
  7. B

    Time dilation in a non-inertial reference frame

    Hi! :smile: Need some help here. Can we perceive time dilation and length contraction in a non-inertial reference frame? If we observe a reference frame experiencing acceleration close to c, do we see the same effects as in an inertial reference frame?
  8. S

    Choice of reference frame in conservation of momentum/energy problems

    Problems related to conservation of momentum/energy can be solved by taking reference frame which is stationary to center of mass or which is stationary to ground/observer. So when to use what frame or which frame is beneficial in which case/type of problems? I m confused !:confused:
  9. Z

    Exploring Inertial Reference Frames in the Expanding Universe

    Are galaxies, quazars inertial reference frame? I think they are at rest or moving at constant velocity relative to the expanding space. But what is the coordinate system to the scale of the whole universe that can describe these inertial reference frames appropriately? Is the coordinate...
  10. M

    The part of relativity I never got, reference frame

    So I was pondering long distance space travel. As I understand it, if you can accelerate a vessel, say over the course of a year, to near light speeds, you can cover very very long distances in a very short period of time(as measured on your on space ship) due to the effects of relativity...
  11. K

    Preserving Magnetic Polarity in a Revolving Reference Frame

    ***not homework for any class*** Title: "Preserving Magnetic Polarity in a Revolving Reference Frame" Problem: How can a revolving reference frame (assuming an uncharged observer with negligible mass) observe the same polarity for a magnet in the case where the rotational speed is great enough...
  12. R

    A sliding puck analyzed from an inertial reference frame

    Homework Statement Located here:http://imgur.com/qP9fd.png" The Attempt at a Solution I don't know how to do this problem. First of all how do I approach it? Should I do a free-body diagram? Should it be done at position 1? How do I account for the different frame of reference...
  13. K

    Pendulum tension in rotating reference frame

    Homework Statement A student is in a rotating chair with a pendulum hanging down in the middle of the rotation. . I need to calculate the difference in tension when the bob is hanging vertically and when the chair is rotating. The length of the bob and string is 65.3 cm. The radius of the...
  14. H

    Electrostatics and reference frame

    Hi, I'm stuck with a question concerning electric fields : Can an electrostatic potential drop exist in (what I would call) a 0 dimensional system ? Let's imagine we are in a region of space where there is nothing but a uniform magnetic field. So the problem is anisotropic but does not...
  15. B

    Problem in inertial reference frame

    Well, in principle, this problem seems very easy but I don't know the exact explanation.Here we go. We have a truck and a pack in its back.The bed of the truck is frictionless and the pack is stopped by a small piece of wood of something like that. The size of the pack is whatever(for...
  16. 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...
  17. 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...
  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. 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...
  20. 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...
  21. 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
  22. 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...
  23. 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...
  24. 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...
  25. 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?
  26. A

    Inertial reference frame for 2&3 law

    Does the concept of Inertial reference frame also applicable for 2nd & 3rd law of motion?
  27. J

    Why no privlidged reference frame?

    I'm not a physicist and not a mathematician. I just want to understand things, and have read "advanced layman" books. It's often touted that Noether's theorem shows that the uniformity of space (the same everywhere; no preferred origin) implies conservation of momentum. More properly, the...
  28. jaketodd

    Relativity of simultaneity implies a universe for each reference frame?

    The fact that the relativity of simultaneity causes events to not happen at the same time, dependent on reference frame, seems to imply a separate universe or world for each and every thing in the universe. Different events at different times due to the relativity of simultaneity would lead to...
  29. K

    C according to what reference frame?

    This question may be nonsensical, but I have to ask. I'm a noob to relativity so please bear with me. All observers measure the same speed of light, correct? We also know that there is no favored frame of reference. So... what is to stop an object from accelerating to 0.95c, taking a...
  30. C

    Is spacetime an absolute reference frame?

    STUPID QUESTION ALERT! Is spacetime an absolute reference frame?
  31. J

    How does the holographic principle relate to the reference frame of a photon?

    So if I'm a fast object moving in a sphere, in my frame of reference the sphere begins to contract along the direction I'm moving. As I approach the speed of light, the sphere begins to deform into a disk. If I'm a photon, the sphere is a disk. Rather than requiring requiring 4 coordinates to...
  32. Y

    Telling if a reference frame is moving or at rest

    As stated in SR and the principle of equivalence, there is no privileged reference frame or reference frame at absolute rest. However, I went across the following idea that seems to be able to tell if a reference frame is moving or at rest. Please help me point out what is wrong in my idea...
  33. B

    Changing the inertial reference frame to follow a mass in a collision

    Homework Statement We could change to inertial reference frame in a collision to follow a mass. But what would the down side be if we did? Homework Equations Vf1=(M1-M2)/(M1+M2)*Vi1 +2M2/(M1+M2)*Vi2 Vf2=2M1/(M1+M2)*Vi1 +(M1-M2)/(M1+M2)*Vi2 The Attempt at a Solution This question...
  34. I

    Communicating Vessels in a noninertial reference frame

    Hello all, Should be a simple question (just started Physics 1 not long ago). Here it is: The thin, fluid filled glass tube is sitting on an accelerating cart. As a result the level of the fluid rises as shown in the picture (attached) by D = 0.6 m. The distance L is given. L = 0.2 m...
  35. fluidistic

    Confused about charged rotating disk-Magnetism, reference frame

    For some reason I've thought about the following case : A uniformly non conductor charged disk is rotating with an angular velocity \vec \omega. If I see it in front of me I'd observe a magnetic field since moving charges produce a current which produce a magnetic field according to Ampere's...
  36. M

    Defining a Lagrangian in an rotating reference frame frame

    Hi I'm trying to define a Newtonian lagrangian in an rotating reference frame (with no potential) Something to note is that the time derivative of in a rotating reference frame must be corrected for by: \frac{d {\bf B}}{dt} \rightarrow \frac{d {\bf B}}{dt} + {\bf \omega} \times {\bf...
  37. D

    Understanding Time: Special Relativity & Earth's Reference Frame

    What does Special Relativity imply about past, present, and future time? So, here on earth, what can be said about our understanding of past, present, and future actions? Within the same reference frame, is time static? Is it ordered?
  38. 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)]...
  39. 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
  40. 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?
  41. 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?
  42. 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...
  43. 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...
  44. 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...
  45. 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...
  46. 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...
  47. B

    Is Poincare Symmetry Fundamental to Relativity as Proposed by Einstein?

    I have heard the following oppinion: Whether a reference frame is inertial is completely determined by whether Newton's laws are applicable for particles moving at low (that is, nonrelativistic) speeds in that reference frame. Do you agree with it?
  48. B

    Showing momentum will be conserved in moving reference frame

    Homework Statement the question gives me the masses and initial velocities of two balls which collide elastically and asks me to prove that it the momentum will be conserved in both a still reference frame and a moving one. Homework Equations The Attempt at a Solution i know that...
  49. jtbell

    How two clocks can each run slow in the other's reference frame

    People often have trouble visualizing how time dilation can be "mutual" in special relativity. That is, if you have two clocks moving with respect to each other, in each clock's rest frame the other clock runs slower. The following example illustrates how this can be possible without...
  50. D

    Simple Reference Frame problem

    Problem If you throw a ball with velocity v at a wall, it rebounds with the same speed, v. What happens if you throw it at speed v towards a wall which is traveling towards you at speed w? What is your answer in the limit in which w is much larger than v? Answer Let us work in the frame of...
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