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. BTBlueSkies

    Free Fall vs accelerated reference frame question.

    I had a though last night that kept me awake trying to figure out what I was trying to understand. I have been out of school many years now so I have forgotten much.. Here is my question. Lets imagine there is a 30 meter diameter hole (complete with a vacuum) in my front yard that goes through...
  2. Calpalned

    A mass m slides in a moving reference frame

    Homework Statement An inclined plane, fixed to the inside of an elevator, makes a ## 32 ^\circ ## degree angle with the floor. A mass m slides on the plane without friction. What is its acceleration relative to the plane if the elevator accelerates upward at 0.50 g? Homework Equations...
  3. P

    The surface of the Earth as a reference frame

    At about 05.30, Dr. Lewin makes a small calculation to find the centripetal acceleration one experiences due to Earth's spin (at the equator). He then says that because of how small the magnitude of this acceleration is, we could consider the Earth's surface to be an inertial reference frame...
  4. M

    Light angles measured in a moving reference frame

    I've managed to get through all of this question without trouble until part d). The full question is given here: I've calculated the "true" angles of Star A and Star B as 71.57 degrees and 45 degrees respectively in Frame S, and the "light" angles should be the same, since the stars are...
  5. M

    Three Reference Frame Relativity Problem - Velocity Addition or Proper Lengths

    Homework Statement Anna and Bob have identical meter sticks. Anna an observer on Earth, sees Bob traveling in a spaceship at 0.5c away from her. Bob leaves his spaceship in an escape pod, moving away from Earth and the spaceship at 0.1c with respect to the spaceship. How long is Bob's meter...
  6. Diploria

    Hafele-Keating with the plane as reference frame?

    Hello, I noticed quite a few questions on the Hafele-Keating experiment here, but I believe none that have my exact question. I understand the explanation given for "a frame of reference at rest with respect to the center of the earth", as in the Wikipedia article. But what happens if...
  7. N

    How Do You Solve a Rotating Reference Frame Problem in Physics?

    Homework Statement I have attached the problem as a picture on this post, am really really unsure on how to start! so far the only thing i can think of doing is using this equation (\frac{d^{2}r}{dt^{2}})_{s} = ( \frac{d^{2}r}{dt^{2}})_{s'} + 2ω \times (\frac{dr}{dt})_{s'} + \dot{ω}...
  8. S

    What is a pseudo-force and how does it relate to non inertial reference frames?

    So I was told that a pseudo-force acts on a body when its's motion is analysed with respect to a non inertial reference frame. I'm a bit confused. Does that mean the reference frame is accelerating with respect to the body, or with respect to the earth? And why does there have to be any sort of...
  9. M

    Basic non-rotating accelerating reference frame problem

    Homework Statement A uniform thin rod of length ##L## and mass ##M## is pivoted at one end. The pivot is attached to the top of a car accelerating at rate ##A##. What is the equilibrium value of the angle ##\theta## between the rod and the top of the car? Homework Equations None in...
  10. E

    Concept of coordinate reference frame in GR

    In SR there is a whole family of so called inertial observers that are defined as those observers that move at relative constant speed with respect to one another, whose descriptions of nature are all equivalent and whose spacetime coordinate are related by Lorentz transformations i.e. those...
  11. M

    Reference frame in relative motion

    I red a classical mechanics concept in a book. Imagine that we have two observers with two frames of reference F1 and F2 observing a particle P in motion. One of the observer is in motion and another is at rest,(lets take F1 is at rest and F2 is in translation motion with velocity V) let r1 be...
  12. WannabeNewton

    Proper Reference Frame -Accelerated observer

    "Proper Reference Frame"-Accelerated observer Hi guys. This is regarding section 13.6 (p.327) in MTW. Here the authors consider an arbitrary accelerated observer in any space-time and construct a set of local coordinates carried along the entire worldline of the oberver with the origin of the...
  13. D

    DQ Reference Frame in VSC Station: Fig. 1(b)

    Each VSC station has the same configuration, and its vectorbased equivalent circuit in the synchronous dq reference frame is shown in Fig. 1(b). Could someone please explain me what doe "dq reference frame" mean?
  14. S

    Use of a non-inertial reference frame in a problem involving rotation?

    Homework Statement A disk rotates with angular velocity ω. It has a groove cut along the diameter in which two blocks of mass m and M slide without friction. They are connected by a light string of length l, fixed by a catch with block m a distance r from the center (r + radius of M = l)...
  15. D

    Reference frame for analyzing ball rolling down incline

    Hi all, I have a question about how to analyze the problem of a ball rolling down an incline plane. Assuming there is friction, at each instant the ball swivels about a pivot point on the incline that is stationary due to static friction. We then would analyze the torques about this point...
  16. 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...
  17. M

    Accelerating reference frame

    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...
  18. 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...
  19. 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
  20. 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.
  21. 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...
  22. 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...
  23. 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 :)
  24. M

    What exactly is an inertial reference frame?

    Due to my job and other classes, I've been studying ahead of my class by myself to not fall behind and I'm not sure if I'm oversimplifying this in my head and not really grasping the idea. Newton's First Law of Motion states that an object with a net force of zero stays in constant motion (or...
  25. C

    Can Earth be considered an inertial reference frame?

    hi guys, i have a basic question on special relativity.. if the inertial reference frame denotes the frames that holds up the Newtonian 1st law, then can Earth be an inertial frame? i mean it changes direction of velocity as it moves in the orbit around sun, so its not in constant velocity ...
  26. A

    Can Light Be the Perfect Reference Frame to Solve Problems of Reference Frames?

    We have a problem of perfect reference frames( according what we are taught in school) If universe is expanding, the so called fixed stars are also moving. According to the special relativity, the speed of light is constant in every reference frame, So if we let light as the perfect reference...
  27. S

    Can inertial reference frame have different sizes at least in theory?

    hi can inertial reference frame be in different sizes at least in theory? i mean that can there be two different frames of reference in same place at same time, where the observer in both frames observes physical laws to be normal in their own frame of reference, but the other frame appears to...
  28. B

    Different times Reference Frame Question

    Homework Statement In a given reference frame, event 1 occurs at t1 = 0 s and position x1 = 0 m while event 2 occurs at t2 = 3.6 × 10^−4 s and x2 = 0.60 × 10^5m. Is there a second reference frame in which these events could be at the same place but different times? If so, specify its motion...
  29. R

    [SR] - Photonic Reference Frame

    Recently learned about Special Relativity, so my brain is running perpetual circles around itself asking questions. So, I figured I would come here and ask where could I find out more information about the Lorentz Factor being undefined at a luminal velocity? Or more basically, where do I...
  30. S

    Question about noninertial reference frame.

    Homework Statement If you are in a noninertial reference frame, that means: Homework Equations The Attempt at a Solution I know that nonintertial reference frame is something that is moving. However, if I am in it, then should I be moving together with it?
  31. V

    Age of the universe in earth's reference frame?

    I understand that the ~14.6 billion year age of the universe is in the cosmological frame, i.e., representing the coordinate time elapsed in a comoving reference frame. Of course this means (as has been discussed plenty of times here) observers in different frames would measure a different age...
  32. E

    Find a vector to a particle from a rotated reference frame

    Homework Statement Consider a particle in space whose position vector from the origin of reference frame i is given by the expression r(Oi to P) = 37t(Ii + Ji + Ki). The distance vector from the origin of another reference frame (m) to the origin of the I reference frame is given by r(Om...
  33. V

    Is reference frame important when looking at work done?

    It must be, right? Obviously, if you're pushing a block by exerting a force F on it over a distance D on the ground, if you are in the frame of you or the block, your distance is 0 so it appears you're doing no work. I ask this question because I was doing a practice problem that should be...
  34. N

    The divergence operator in a rotated reference frame

    One can easily prove that \nabla \cdot f is invariant under a rotation of the reference frame, however I would like to prove that the divergence operator itself is invariant (same principle, different approach). In other words I want to prove that \mathbf \nabla = \mathbf e_x...
  35. Telemachus

    Generalized momentum and Hamiltonian over a non inertial reference frame

    Hi there. I need help to work this out. A particle with mass m is studied over a rotating reference frame, which rotates along the OZ axis with angular velocity \dot\phi=\omega, directed along OZ. It is possible to prove that the potential (due to inertial forces) can be written as: V=\omega...
  36. aleemudasir

    Object moving at speed of light as Reference frame.

    Is there any other object except photon which moves at the speed of light? Why can't an object moving at the speed of light be taken as reference frame? Can we use the equation m=m(0)/sqrt(1-v^2/c^2) for an object moving with speed of light?
  37. S

    Basic question about inertial reference frame

    I have no background in relativity. Recently I started reading some introduction to special relativity in Griffith's EM book, where he vaguely defined an inertial reference frame as one in which Newton's first law holds. Now according to this definition, does such frame exist in nature? On...
  38. L

    Non inertial or inertial reference frame?

    Homework Statement Specify and explain whether the following is an inertial or non-inertial observer: An observer is placed on a rock between Andromeda and the Milky Way. Homework Equations N/a The Attempt at a Solution So here is my understanding, the observer would be situated...
  39. B

    Does the energy of light depend on the observer's reference frame?

    Hi, Physics Forums! This is my first post here and I know just about zero physics, so I apologize in advance if the question is a little daft/naïve. Ok, so here's what I'm wondering: suppose you have a light source that produces EM waves in all directions at some frequency ν, and a camera set...
  40. P

    The relationship between coordinate systems and reference frame

    Hi there, I am confused about the relationship between coordinate systems and reference frame in GR. I understand the coordinate systems can be used to describe reference frames, for example, Local inertial frames in GR can be defined by Riemann Normal Coordinates. However, take the...
  41. B

    Magnetic force in a moving inertial reference frame

    A charged particle is placed next to a current-carrying wire. The wire produces a magnetic field, but if the particle is at rest, the field exerts no force on it. However, in a different inertial reference frame moving at speed v parallel to the wire, the particle is seen to be in motion, and so...
  42. M

    Torque in a non inertial reference frame

    Hi, This is partly inspired by the questions in the thread about normal forces on a cornering car but I thought I'd post here instead of mix that thread up with my question. So suppose we have a biker leaning into a corner. There are the normal force and the force of friction which act at the...
  43. E

    Is the Radial/Transverse coordinate system a non-inertial reference frame ?

    Hey guys, I am having some problems with the concept of inertial/non-inertial frames of reference and their applications in engineering dynamics. So I've learned that a given frame of reference is defined to be non-inertial when something in the studied system can only be explained through...
  44. S

    Local Reference Frame: Explaining What It Is?

    According to this, if someone spins around at 2 revs per second when the moon is in the horizon, the moon seems to move at 4 times the speed of light. And this implies the moon is not in our local reference frame. And per this, local inertial frame applies to "small regions of a gravitational...
  45. K

    Find a reference frame where momenta of electron and proton are equal

    Homework Statement The electron is traveling at a speed of β=.9999999, γ=1957, with mass mc^2=.51099 MeV. The Proton is traveling at a speed of β=.9, γ=2.29, with mass mc^2=938.27 MeV. They are heading in opposite directions, directly towards each other on the x-axis Find the reference...
  46. R

    Reference frame for harmonic motion.

    If you a mass being accelerated by a force which is acting upon a spring attached to the mass it will exhibit harmonic motion. However unlike a fixed harmonic oscillator there is no explicit solution to the equation which describes the motion of the mass in a reference frame outside of the...
  47. H

    Determine the velocity of a reference frame S

    Can someone give me a clue/hint to finish this question? "In a reference frame S, the electric and magnetic fields of an electromagnetic wave E and B are perpendicular to each other. Determine the velocity of a reference frame S' in which (a) E' = 0 and (b) B' = 0"
  48. G

    A question about stationary reference frame

    Is this correct? There are two clocks on Earth that are synchronized. One clock goes out on a spaceship at .8c. Now according to the stationary or Earth FOR one year goes by for its clock but he sees that only .6 of a year has gone by on the clock of the spaceship. Now the spaceship...
  49. S

    Velocity of a photon from its own reference frame

    So what will it see it self as?? At rest or moving a velocity c? Either way it seems to be a contradiction, so does that mean a photon can't be reference frame?
  50. U

    Observation from Single reference frame and STR

    Last thread that I initiated was titled `Simultaneity is directional while Time Dilation is not', which presented a scenario for the Non-directional property of Time Dilation in STR. Which I think, needs to be reconsidered. And I believe this is the reason why `STR can only be worked out when we...
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