What is Reference frames: Definition and 227 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. L

    I Why Does GR Not Allow Global Reference Frames?

    Under SR, we can talk about inertial frames that apply globally. However apparently, under GR, this concept only applies locally, because it breaks down on larger scales. Can anyone provide an explanation as to why this is? Is this due to the fact that space-time is warped in GR?
  2. T

    Proper movement, reference frames and gravitational waves

    Hi, So apparently electrons don't orbit the nucleus of atoms so I'm assuming the lack of movement means that no energy from the atom is radiated away from an atom due to minuscule gravitational waves, over the life of the universe. But gravitational waves have got me thinking about reference...
  3. C

    Does the bullet reach its target?

    Homework Statement As outlaws escape in their getaway car, which goes 3/4c, the police officer fires a bullet from a pursuit car, which only goes 1/2c. The muzzle velocity of the bullet (relative to the gun) is 1/3c. Does the bullet reach its target according to Galileo? According to Einstein...
  4. C

    What must be one's speed, relative to a frame S, in order....

    ... in order that one's clocks will lose: (a) 1 second per day as observed from S? (b) 1 minute per day as observed from S? I was referencing this:( http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/tdil.html#c2 ) hyperphysics page but I still can't seem to understand what I need to do to...
  5. A

    How a rotational motion could be in an inertial ref. frame

    When rotation exists, so does the radial acceleration. It can be defined as ar=-ω2xr So there is a kind of acceleration with rotation all the time. Thus, we have to use non-inertial reference frame all the time. Could a rotational movement be analysed in an inertial ref. frame?
  6. B

    Time Dilation: Rel. Ref. Frames and Universal Reference Frame

    I understand that if someone is traveling away from Earth at a very high speed, time will slow down for the traveler relative to the people on earth. However, why is it not the other way around? If there is no universal reference frame, could this situation not also be thought of as the traveler...
  7. Raymond Potvin

    B On light clocks and reference frames

    I had this questioning about the light clock on another thread, and DaleSpam suggested that I open my own thread, so here it is. I was asking if the light clock mind experiment was not contradicting the reference frame principle. I added that to my drawings: And DaleSpam answered this: So...
  8. S

    Definition of a specific kind of motion

    Homework Statement It is not really a homework question, but rather a translation problem. I searched everywhere, but I still cannot find a good translation into English of a term that is defined as: "In mechanics, the motion of a moving reference frame relative to another (primary) reference...
  9. 0

    Invariance of Acceleration in Inertial Reference Frames

    Claim: The acceleration (both direction and magnitude) for any object is the same in any inertial reference frame. Is this claim true? I think it is, but someone mentioned to me that time may be an issue as it's not agreed upon in all inertial reference frames. I'd appreciate any references...
  10. W

    Time Dilation & Acceleration: Leaving Earth Effects

    Leaving Earth at constant acceleration will make time on board go slower. Acceleration will take the ship closer and closer to c Question is: How long will acceleration act on the ship? The time as measured on Earth or on the ship? The final v will be greatly different. Of course, given enough...
  11. pixel

    Properties of light in 2 moving reference frames

    In the usual derivation of time dilation in special relativity, we have two frames of reference, A and B, moving relative to each other with velocity v. In A's frame, a light beam is directed vertically upward toward a mirror and reflected vertically back down. In B's frame, the light follows a...
  12. D

    Lorentz scalars - transformation of a scalar field

    When one considers a Lorentz transformation between two frames ##S## and ##S'##, such that the coordinates in ##S## are given by ##x^{\mu}## and the coordinates in ##S'## are given by ##x'^{\mu}##, with the two related by x'^{\mu}=\Lambda^{\mu}_{\;\;\nu}x^{\nu} then a scalar field ##\phi (x)##...
  13. R

    Time dilation in accelerating reference frames

    Sorry for the lame question, but I was wondering if someone could help answer the following. I have two synchronised clocks which I place on two different space ships which then accelerate away from me at the same rate and time until they reach a given speed. Ship A then slows down to be at...
  14. 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...
  15. S

    Inertial and Non-Inertial Reference Frames

    Hi All Physics newbie here... Just a quick question regarding Inertial and Non-Inertial Reference Frames. From what I understand: Inertial = One that obeys Newton's Law of Inertia. Moves at constant velocity in one direction Non-Inertial: One that accelerates. Right? So, I read somewhere that...
  16. B

    Fixed and Moving Reference Frames for adding speeds

    Hi Folks, I have some misunderstanding how one can add velocities of different coordinate systems. Consider a planet gear rotating about its own axis and also rotating on its carrier so that the so called velocity of the planet gear relative to the carrier is the planet local velocity minus...
  17. T

    Understanding Torque and Reference Frames in Rotational Motion

    Hello, I have a question regarding the concept of torque and reference frames. Say for example I have a rod of length L and that the rod has it's right side anchored to act as a pivot point. Now let's say that I input a force on the left side of the bar in an upward direction. Assuming that...
  18. L

    What is a Frame of Reference in Physics?

    I'm studying special relativity for the second time and there's something I think I didn't get since I studied classical mechanics: the idea of a frame of reference. I think the underlying idea is that of a point of view, so that we want to study some phenomenon, but we have to observe it so...
  19. I

    The Paradox of Inertial Frames: Exploring the Limits of Classical Physics

    I'm reviewing physics after ~30yrs of neglect, starting with Halliday & Resnick (and the internet). Here's what I understand to be standard Newtonian/classical inertial frames: 1. There exists a set of reference frames, called inertial frames, in which mass, time, force, acceleration, etc. are...
  20. throneoo

    Definition of inertial reference frames

    What is the definition of an inertial frame ? I've read that Inertial frames are reference frames in which Newton's first law applies (i.e.bodies subject to zero net external force moves at constant velocity) , however Newton's 1st law itself is only valid under inertial frames. I find it weird...
  21. Amaterasu21

    Question about rotating reference frames

    Hello, I have a few questions about rotation and relative motion. Suppose we transport the proverbial spinning ice skater used to demonstrate conservation of angular momentum to beginning physics students to a universe with only her and two planets. She is now spinning in deep space...
  22. K

    Inertial frame of reference question for stacked boxes

    Hello, I was wondering about a question and how it would be reconciled within Newton's laws of motion. Take a case where two boxes are stacked on top of each other, and the bottom box rests on a frictionless surface. Now, imagine a rope is attached to the top box, and tension is applied to...
  23. DiracPool

    Relativity Musings: Gravitation, Acceleration & Inertial Ref Frames

    I have a 3-pack of related relativity musings I was hoping someone(s) could enlighten me on: 1) Since the reach of gravity is infinite and the universe is homogeneous and isotropic with regards to the distribution of matter, is it fair to say that no object, even those in deep interstellar or...
  24. A

    Gravity: Conservative or Non-Conservative?

    We generally take the force of gravity to be conservative, but what if the source of gravity is moving through space? Then the force would only be conservative relative to the source, correct? As another example, consider someone in a balloon ascending with constant speed relative to earth...
  25. T

    Reference Frames: Up and Down a River

    Homework Statement A water spider maintains an average position on the surface of a stream by darting upstream (against the current), then drifting downstream (with the current) to its original position. The current in the stream is 0.408 m/s relative to the shore, and the water spider darts...
  26. B

    Question concerning speed of light in reference frames

    My friend posed a question to me that I was unable to succinctly answer (or answer at all for that matter). So I thought I'd make an account and ask people who know more about this than I do. Ok. So let's assume that Person A starts at Position 1. Person B is at position 2, which is 1 light...
  27. E

    A little confusion on reference frames

    In college physics 1, I think I'm confusing myself on reference frames, and would like for one of you significantly smarter persons to let me know if I'm on the right path with understanding it, and if not, could point me in the right direction :) We're just beginning inertia and momentum in...
  28. M

    Reference Frames with Different Origins

    Homework Statement Alex is born in a spaceship and Bill is born on Earth just as Alex’s spaceship passes Earth at 0.90c when t=t’=0 (event A). Planet Z is at rest in Bill’s reference frame (x,ct), where it is 45 light-years (ly) away. Alex, whose spaceship is at rest in the frame (x’,ct’)...
  29. F

    Conservation of energy/momentum and difference reference frames

    I managed to confuse myself with a simple thought experiment. I have a spaceship that uses mechanical springs loaded with balls for thrust. We start in a reference frame O where the ship isn't moving and fire one spring, which gives the ship a velocity v. Pick a new frame O', moving at v in...
  30. P

    Transformation of acceleration between two reference frames

    hello i want to derive the Transformation of acceleration between two reference frames i searched in internet and found a book but i don't understand just one step i attach a picture so you can see what i found in the internet my problem is eq. (1.10) \begin{align}du=\frac{dU}{\gamma...
  31. Feodalherren

    Relativity - time in different reference frames

    Homework Statement An astronaut is traveling in a space vehicle moving at 0.500c relative to the Earth. The astronaut measures her pulse rate at 75.0 beats per minute. Signals generated by the astronaut’s pulse are radioed to the Earth when the vehicle is moving in a direction perpendicular to...
  32. W

    Relative motion of two reference frames

    Homework Statement Two clocks located at the origins of the K and K' systems (which have a relative speed v) are synchronized when the origins coincide. After a time t, an observer at the origin of the K system observes the K' clock by means of a telescope. What time does the K' clock...
  33. S

    Collisions, Impulse, and Reference Frames

    A racquet ball with mass m = 0.245 kg is moving toward the wall at v = 15.4 m/s and at an angle of θ = 28° with respect to the horizontal. The ball makes a perfectly elastic collision with the solid, frictionless wall and rebounds at the same angle with respect to the horizontal. The ball is in...
  34. B

    Time Lapses In Two Different Reference Frames

    Hello, I would like to prove that the time experienced in a moving reference frame is longer than in a stationary frame. Here is my solution: Suppose that at time t = 0 two reference frames, S and S', origins coincide; similarly, the x,y, and z axes of the S-frame overlap with the...
  35. F

    Change in kinetic energy between reference frames

    I was trying to do some studying regarding the definitions of energy, and I've hit a road block. I know that since velocity is frame-dependent, an object's kinetic energy as observed in two different frames will yield two different results. My initial expectation was that changes in...
  36. PeroK

    Simultaneity between events in reference frames

    Hi, I've been trying to understand the (lack of) simultaneity between events in reference frames moving wrt each other. I'd be grateful if someone could confirm that I've got things right: If two events are simultaneous in one reference frame (S'), then they will not be simultaneous in a...
  37. H

    Rotating reference frames and acceleration

    My question stems from a conversation I had recently with another physics buddy of mine and has to do with rotating reference frames and acceleration. Say, in a non-rotating reference frame you have an object with a known position. For the sake of argument, say it has a position A of 0i + 2j +...
  38. D

    Understanding non-inertial reference frames in CM and SR.

    Sorry if this is a frequent topic, but I think it's interesting and probably worth repeating if it's come up often before. Let me lay out my question by example (and if anything is inaccurate feel free to point it out), and then I'll summarize at the end. It's easy to show in Classical...
  39. A

    Kinetic Energy in Reference Frames

    K'sys=1/2MtotalVcm2+1/2\muVreli2 I understand this equation represents the total kinetic energy in a reference frame. What I'm not getting out of this is the overall concept. I understand that the first part of the equation is supposed to represent the total kinetic energy required to...
  40. A

    Inertial reference frames in general relativity

    Hi guys, I was reading some stuff about general relativity and the first impression is that isn't completely the follow-up to SR. In what I've read it has a different assumption about inertial frames, that they are only significant only locally. What does this really mean and what are the...
  41. A

    Interchanging a position between two reference frames?

    \vec{r}_a is a positional vector from reference frame a. What is the position of same point from reference frame b ? If required, assume position of origin of frame a is \vec{m} and unit point (i.e. \langle 1,1,1\rangle_a ) is \vec{n} from reference frame b. I am studying Kleppner and Kolenkow...
  42. S

    Motion of Reference Frames wrt each other

    I am currently working on a Python script to simulate motion of reference frames wrt each other, and I need some help with the math. Here is the problem statement- Suppose I have a frame A A frame B frame B's origin has pos-vector PB,A (function of time) wrt A in frame A frame B is...
  43. 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...
  44. 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...
  45. 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...
  46. 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...
  47. 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...
  48. 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...
  49. 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...
  50. 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...
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