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. Swag ranger

    Acceleration in an inertial reference frame

    Homework Statement 3. (a) If an object's acceleration is zero in one inertial reference frame then is its acceleration zero in all other inertial reference frames? (b) If an object's velocity is zero in one inertial reference frame then is its velocity zero in all other inertial reference...
  2. B

    Twin Paradox from Moving Reference Frame- Return Journey

    Homework Statement a) Alice is observing a small ball of mass m in relativistic motion bouncing elastically back and forth between two parallel walls separated by a distance L with speed u. After each collision it reverses direction, thereby creating a clock. What does Alice observe as the...
  3. M

    A Explaining the Geocentric Celestial Reference System

    Hi there guys, I was wondering does anyone have a layman's explanation of the GCRS as defined in the title. I am confused as to whether this is an inertial or non inertial system. In text modern reference books such as this (chapter 10, section 10.3.2) they define rotating/non rotating...
  4. J

    Is free fall NOT the same as floating in space?

    For many, many years (don't ask), I've been running into the classic example of the local reference frame: the man in the box who can't tell if he's floating free in space, or falling into a gravity well. It occurs to me that if one is in a falling box, a mass released at the top of the box...
  5. Robert Shaw

    I Do we need a reference frame in Quantum Hilbert space?

    Entangled states are only separable relative to certain basis states. So does that mean that reference frames have importance beyond those in spacetime?
  6. Cutetys

    Zero momentum reference frame and an inelastic collision

    Homework Statement In my reference frame, I see two carts collide. Both cart A and Cart B have a mass of 2 kg. Cart A has initial velocity v= 3 m/s i-hat + 2 m/s j-hat, cart B has initial velocity v= 3 m/s I-hat + 4 m/s j-hat. 12 J are released in the collision. In previous parts of this...
  7. S

    Inertial Reference Frame Proof

    Consider a specific reference frame (0XYZ) attached to Earth. A point (origin) being selected, coordinates are ascribed along with a vector basis. This reference is non-inertial because it is locked to Earth and the acceleration of Earth is not zero. Suppose upon rising one morning I felt...
  8. T

    Basic Question about Relativity Reference Frame Shifts

    Homework Statement I'm using Shankar's Introductory Physics course and I can't get a question out of my head regarding his setup of Relativity. There are two observers, S and S'. Observer S is stationary, while Observer S' is sliding past S (to the right) with velocity u. They agree to set...
  9. rumborak

    Magnetic field = electric field in some reference frame?

    This Wikipedia article https://en.m.wikipedia.org/wiki/Relativistic_electromagnetism seems (to me) imply that there is always a frame of reference in which a magnetic field can be rather viewed as an electric field modified by relativistic considerations. Is that always true? That is...
  10. Umrao

    SR: Does observation change when changing reference frame

    Homework Statement Special relativity: A rod traveling with the relativistic velocity of 0.866c moving towards a garage. The length of the rod is L, that of the garage is L/2. From the reference frame of the garage, we find the value of Lorentz factor = 2 we say that rod would fit inside garage...
  11. Pushoam

    Speed of a wave on a string w.r.t. which reference frame

    Speed of a wave in a string is given by √(τ/μ) . But this speed is with respect to which reference frame? Since, the speed depends on τ and μ( which are independent of reference frame ), I can consider speed of wave independent of reference frame. But this is not so. From experiment, we know...
  12. Isaac0427

    Can you know which reference frame is accelerating?

    Person A is in car A and person B is in car B. These people don't know if their car is moving (i.e. there is no scenery and their engines don't vibrate or make noises). Car A is stopped and car B is moving with a velocity v. Person A thinks that car B is moving with a velocity v while person B...
  13. Pushoam

    I Measuring Wave Speed: Reference Frame Considerations

    In the wave equation## \frac {\partial^2 \psi} {\partial x^2}=\frac{1}{v^2}\frac{\partial^2 \psi}{\partial t^2}\tag{1}##, v is the speed of the wave propagation. With respect to which reference frame is this speed measured( in general)?
  14. I

    I Acceleration towards c without a reference frame and changes

    Hello everyone. Below are two problems I have been thinking about lately. Let’s consider two cases: we have a spaceship surronded by an utter void - nothing outside which the spaceship’s pilot could refer to. The pilot (in his robotic body, allowing him to withstand enormous G-forces) turns on...
  15. L

    I Reference Frame Usage in General Relativity

    In the book General Relativity for Mathematicians by Sachs and Wu, an observer is defined as a timelike future pointing worldline and a reference frame is defined as a timelike, future pointing vector field Z. In that sense a reference frame is a collection of observers, since its integral lines...
  16. Cathr

    B Special Relativity Q: Choosing Light as Ref

    Special relativity states that the speed of light is constant for all the references, as long as they are not accelerating. For example, the speed of light would be c for a train moving linearly with a constant speed and would also be c for an observer who's not moving at all (I took the Earth...
  17. bananabandana

    Transforming to a Rotating Reference Frame

    Homework Statement Let ## \mathbf{r} ## be the position of a point in a rigid body relative to some origin ##O##. Let ##\mathbf{R}## be the position of the centre of mass from that origin. ##\mathbf{r^{*}} = (\mathbf{r}-\mathbf{R})##. ## d\boldsymbol{\phi} ## is the infitesimal vector directed...
  18. ElPimiento

    Puzzled by an equation for relativistic time difference....

    Homework Statement Suppose that A', B', and C' are at rest in frame S', which moves with respect to S at speed v in the +x direction. Let B' be located exactly midway between A' and C'. At t' = 0, a light flash occurs at B' and expands outward as a spherical wave. (A', B', and C' are all on...
  19. nagyn

    Distance between two events in a moving reference frame

    Homework Statement Observer O at the origin of a coordinate system is at rest relative to two equidistant space stations located at x=+3.00×10^6km (station A) and x=−3.00×10^6km (station B) on the x axis. In reference frame O, station A sends out a light pulse at t = 0 (event 1) and station B...
  20. Arman777

    I Can Spacetime be a Reference Frame?

    I was watching one of the documentaries of Brian Greene (Beyond Cosmos). here at (12:00-12:10) he says.The skater spins respect to space. My question is How can space-time can be a referance frame itself ? Is it means we can just pick a coordinate and make it a referance frame ? (Sounds...
  21. P

    I DDWFTTW: Looking for the least confusing explanation

    I have tried to find the least confusing (or rather, the most 'deconfusing') explanation for why it is possible for a cart with a prop to travel directly downwind faster than the wind. So far this is what I've come up with: Initial discussion At first glance, a cart traveling down faster than...
  22. E

    How quickly are you moving relative to the ground?

    Homework Statement On a long bus ride, you walk from your seat to the back of the bus to use the restroom. The bus is driving at 120 km/h , and you walk at 2.5 m/s from your seat to the restroom. How quickly are you moving relative to the ground? Homework Equations vpg=vpb+vbg The Attempt at a...
  23. E

    Determine the location of the center of mass of spheres

    Homework Statement All three disks are made of sheet metal of the same material, and the diameters are 1.0 m , 2.0 m , and3.0 m . Assume that the x-axis has its origin at the left-most point of the left-most object and it points to the right. Part A) Determine the location of the center of mass...
  24. E

    Find the centre of mass of the system?

    Homework Statement All three disks are made of sheet metal of the same material, and the diameters are 1.0 m , 2.0 m , and3.0 m . Assume that the x-axis has its origin at the left-most point of the left-most object and it points to the right.Determine the location of the center of mass of the...
  25. J

    Momentum and Inertial Reference Frame

    Homework Statement At the roller rink, two 20-kg girls accelerate toward each other until they are each moving at 2.7 m/sin the Earth reference frame. They then collide stomach-to-stomach, grab on to each other, and fall to the floor. A. Calculate the magnitudes of the momentum of each girl...
  26. S

    I Polarization in laterally moving reference frame

    Imagine that you are sending photons that are polarized at ##45^\circ##, towards a detector that you are facing (e.g. the detectors's input face is parallel to your device/computer screen right now). The detector's polarization axis is also oriented at ##45^\circ##, so all the photons are...
  27. X

    Momentum with Two Carts on a Low-Friction Track

    Homework Statement A student runs an experiment with two carts on a low-friction track. As measured in the Earth reference frame, cart 1 (m = 0.48 kg ) moves from left to right at 1.0 m/s as the student walks along next to it at the same velocity. Let the +x direction be to the right. A. What...
  28. E

    B GR: Using Earth as a Reference Frame - Q&A

    I'm trying to get my head around GR. As I understand it, any frame of reference is as valid as any other for modeling the universe. Therefore, it is valid to use a non-rotating Earth as a frame of reference, and try to model the movement that is seen from this frame. But if that is true, I...
  29. pixel

    I Earth as Inertial Ref. Frame: Test Relativity's Precision

    Special relativity is one of the most tested theories in physics. A central postulated of SR is that the speed of light is the same for all observers in inertial reference frames, and this leads to time dilation and the other effects that have been tested with a high degree of precision. We...
  30. T

    I Time in gravitational reference frame?

    Hi, so Newton said that gravity was like or equivalent to a force? When I learned about SR we were talking about the passing of time as defined by a photon bouncing between two parallel mirrors. So when we're sitting our two parallel mirrors in a gravitational field, even though I suppose...
  31. hackhard

    How to check if frame is inertial?

    inertial frame is one in which isolated particle has constant velocity but is there actually any "isolated particle " ? how then can frame be defined as or not being inertial ? or is it that - for a system in which acceleration due to external forces is equal for all members , the frame of...
  32. hackhard

    B Why not the sun revolves around the Earth?

    why was Earth considered to revolve around the sun and nt the other way round? why is it wrong to analyze planetary motion from Earth frame?
  33. hackhard

    B Can body start spinning without ext cause

    suppose a platform "P" is rotating about the z-axis wrt x-axis . another platform "Q" rotating about z-axis below "P" with same angular velocity wrt x-axis standing on Q , P is at rest wrt Q, After some time rotational inertia of P about z-axis starts changing with time standing on Q , P will...
  34. B

    Acceleration in a non inertial reference frame

    Homework Statement A platform rotates with ##\omega=10## rad/s around ##z##-axes. A ball is connected, with a yarn to ##z##. Its distance to the axes is 15 cm and it rotates with ##\omega=10## rad/s. There isn't friction between platform and ball. Suddenly, the angular velocity of the...
  35. REVIANNA

    Momentum in centre of mass reference frame

    my book says " the total momentum is zero in the centre of mass reference frame.This should not surprise you" but ITS NOT INTUITIVE FOR ME. I am considering a completely elastic collision. 1. I know the v_cm is const because there are no ext forces on the system of the two masses undergoing 1D...
  36. sandyforever

    Is force independent of reference frame?

    Homework Statement Recently, I have been wondering whether forces are independent of reference frames(inertial and non inertial). From Newton's law we know that the second law is valid only for inertial frames. But what about the non inertial frames. Let ∑F be the net force on an object in an...
  37. V

    Determining Position and Center of Mass using Reference Frame

    Homework Statement Homework Equations Xcm = (x1m1+x2m2) / (m1+m2) The Attempt at a Solution ok so I'm having trouble understanding what's happening in the question... when the penguin moves, is the sled also moving? If it's friction less ice then if the penguins moves L, the sled will...
  38. Pejeu

    Spaghettification and gravity in theory of relativity?

    Per my layman's understanding, the apparent force of gravity, as explained by the general theory of relativity, is actually the result of rectilinear motion at uniform speed through warped spacetime. 1. If that's the case, what actually causes gravity for objects at rest with respect to the...
  39. D

    Simultaneity: disagreement, in the same reference frame

    Hello PF. There are two lightning flashes , and two stationary observers. Observer 1 who is equidistant from the flashes, sees them as simultaneous Observer 2 stands one step to the side of observer 1, and is not equidistant. He sees the flashes as separate, the light having unequal distances...
  40. J

    What's the reference frame for the universe as a whole?

    I'm just beginning physics and teaching myself classical physics from an intro physics textbook and in the 2nd chapter it described reference frames. This got me thinking. My reference frame is the earth, as that is what I use to describe position, displacement, ect. But what is the reference...
  41. E

    Conservation of energy in a moving frame

    I know a similar question has been asked but I'm still kind of stumped. Imagine the Earth on the left and a small mass to it's right separated by some distance h. You are in the frame of reference where the Earth and the small mass are moving to your right at some speed v. So, both the Earth...
  42. G

    From RTN reference frame to ECI and orbital elements

    Hi all, I'm curently meeting the following problem and can't figure it out by myself. Assume we have to vehicles in space, a target and a chaser spacecraft . The target spacecraft defines the RTN frame of reference. Given the position and velocity of the chaser in RTN-coordinates, how can I...
  43. Tonia

    Show that Newton's 2nd Law is *Not* valid in a reference frame

    Homework Statement Show that Newton's Second Law is NOT valid in a reference frame moving past the laboratory frame of problem 1 with a constant acceleration? Problem 1: In a laboratory frame of reference, an observer notes that Newton's Second Law is valid. Show that it is also valid for an...
  44. Tonia

    Show that Newton's 2nd Law is Not valid in accelerating reference frame

    Homework Statement Show that Newton's Second Law is NOT valid in a reference frame moving past the laboratory frame of problem 1 with a constant acceleration? Problem 1: In a laboratory frame of reference, an observer notes that Newton's Second Law is valid. Show that it is also valid for an...
  45. Tonia

    Show that Momentum is conserved in a reference frame

    Homework Statement https://answers.yahoo.com/question/index?qid=20150607101609AAs8C9t Show that momentum is conserved in a reference frame moving at 10.0 m/s in the direction of the moving car. Homework Equations Mass M for 2000 kg car, Mass m for 1500 kg car. To the observer on the ground...
  46. Mysteryciel

    Kinetic Energy and Reference Frame

    I know that kinetic energy depends referance frame is there any article about this issue thanks ?
  47. Mysteryciel

    Can the CMB Reference Frame be Changed in the Newtonian Friedmann Equation?

    I know that in physics we can change referance frame.The Newtonian Friedmann equation is ##H^2-{8πGp /3}={-k/a^2}## I know that this equation derived from CMB referance frame.Now can we change this referance frame ? (And If you can give me an article about this issue I will be very happy,I...
  48. Andre' Quanta

    Distinction between coordinate and reference frame

    How is it possible to distinguish a change of coordinate from a change o reference frame? I had this problem while i was studying Rindler' s coordinates: is it only another way to describe a Minkowsky space-time region or does it rappresent a region of the space time as described by an...
  49. Quarlep

    Some Interesting Problems (Reference Frame)

    I have some question about referance frame 1-Is physics works without referance frame ? 2-Is Space-time itself can be a referance frame ? I mean "Earth speed, relative to arbitary point in space time, is 100.000 km/s" Is this sentence make sense to physics ? Or we need an object to make a...
  50. Calpalned

    Velocity on a moving reference frame

    Homework Statement I am reviewing for my midterm and I just want to quickly understand a concept. It seems that velocity does not depend on the original reference frame. For example, let's say spider man is standing on the ground next to a 78.4 meter tall building, and it is known that if he...
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