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. Q

    Magnetic dipole in two reference frames (special relativity problem)

    Homework Statement An EM wave traveling in vacuum has a magnetic field in the lab frame K which is given by \vec{B}(\vec{x},t) = \hat{z} B0 \cos{kx-\omega t} where Bo, k are positive constants and omega = ck. a) A point magnetic dipole, m, where m = \hat{y}m0 (m0 constant) is at rest in...
  2. N

    What is the relative velocity of the two reference frames?

    Homework Statement A particle as observed in a certain reference frame has energy 5GeV and momentum 3GeV. what is the energy in a frame in which its momentum is equal to 4GeV/c? what is its rest mass? what is the relative velocity of the two reference frames? Homework Equations The Attempt at a...
  3. T

    Special relativity question - reference frames

    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. 1. According to an observer...
  4. U

    Relative acceleration between intertial reference frames?

    Does special relativity hold between two inertial reference frames that are undergoing relative acceleration? For example, consider two spaceships traveling toward each other on parallel (but not collinear) trajectories. They would pass each other at some non-zero distance, and thus their...
  5. L

    SR, electromagnetic waves in moving reference frames.

    Homework Statement Not really a homework/coursework problem, I'm just trying to make sense of some class notes from our chapter on special relativity. I'm trying to find the expression for electromagnetic wave propagation in a reference frame S' that is moving at a constant velocity with...
  6. W

    Cons. Angular Momentum & Reference Frames

    Hi! I'm currently a student taking a classical mechanics course. Finals are coming up, and I've come to realize that I seem to have a firm grasp of most of the material (energy, forces, etc...) but not momentum. I know this because I was flabbergasted by a problem on my last midterm that...
  7. Z

    Lorentz Transformations and Reference Frames Problem

    Homework Statement In the old West, a marshal riding on a train traveling 35.0 m/s sees a duel between two men standing on the Earth 55.0 m apart parallel to the train. The marshal's instruments indicate that in his reference frame the two men fire simultaneously. (a) Which of the two men, the...
  8. J

    How Do Rotating Reference Frames Affect Forces on a Merry-Go-Round?

    Looking down from a stationary tree branch, a merry-go-round spins in a counterclockwise direction with an angular velocity of 1 radian per second. a squirrel of mass 0.2 kg sits on the outer rim of the merry-go-round, at a radius of 2.0 meters. a) what is the magnitude and direction of the...
  9. J

    Inerital vs Non inertial reference frames: quick conceptual question

    Homework Statement I'm doing a problem in which an ant crawls in a circle on a spinning pottery wheel. Say I'm looking at the friction which holds the ant in place. It keeps the ant from slipping. Looking at it in the inertial frame of reference, I know that the centripetal force points...
  10. A

    Why is the speed of light same in all reference frames?

    kindly be descriptive
  11. A

    Events in different reference frames

    I am having trouble with measuring coordinate time in different inertial reference frames. For example: Say a car is driving around a circular track (at constant v) and passes a stationary observer. I'll call this event A. Then the car makes another lap and passes the observer again (Event...
  12. 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)...
  13. 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?
  14. 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...
  15. 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...
  16. 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...
  17. 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...
  18. 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...
  19. 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...
  20. 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...
  21. J

    Lorentz transformations ( synchronising reference frames?)

    Lorentz transformations ("synchronising" reference frames?) Homework Statement A particle moves from (x,y,z,t) = (0 m,0 m,0 m,0 s) to (1 m,1 m,0 m,10 ns). i. What is the speed of the particle in this reference frame? ii. What is the speed of the particle in a reference frame moving...
  22. D

    Bullet vs Photon: speed of light, momentum and reference frames

    X________________ moving | observer | | ---> v (moving speed train) photon | ^________________| X________________ ^ moving | ^ ^ observer | d1 ^ ^...
  23. D

    Velocity of rain in different reference frames

    I'm having some trouble with the below vector question. I've got an answer although I'm not sure if it is correct or not. Homework Statement A car travels due east with a speed of 40 kph. Rain drops are falling at a constant speed vertically with respect to Earth. The traces of the rain...
  24. U

    Can objects move faster than the speed of light in certain reference frames?

    Here's a question that's bothered me for a while. Suppose you are a person (P) at point A. You travel between point A and B at some fraction of c (speed of light). And so relativity kicks in. Now, that's the standard relativity model and we talk about P with regard to A and B. Now, what...
  25. Z

    How does the principle of Reference Frames work?

    How does the principle of "Reference Frames" work? What would be an appropriate answer for that statement? I can't think of anything fitting, also I'm not too educated in that subject. Any help is greatly appreciated. :)
  26. K

    Time dilation and non inertial reference frames.

    Homework Statement A clock chimes every hour, on the hour in it's rest frame, is it possible for an observer to measure the time between chimes less than an hour? Homework Equations t = \gamma t0 The Attempt at a Solution I understand that if an observer traveling in the frame S'...
  27. LarryS

    Can the SR Concept of Reference Frames be Applied to Quantum Mechanics?

    SR "Reference Frames" in QM ? The SR concept of “Reference Frame” cannot be transferred to the micro-world of QM because, due to the HUP, space and time are blurry in that world. Comments? (Thanks in advance).
  28. S

    Relative acceleration & reference frames

    Homework Statement 1. You are passing another car on a highway and determine that, relative to you, the car you pass has an acceleration toward the west. However, the driver of the other car is maintaining a constant speed and direction relative to the road. Which of the following statements...
  29. Z

    Understanding Magnetism in Different Reference Frames

    What if i was traveling in a car with an e- with me. W.r.t to a positive charge at rest , it would seem accelerating to me i.e. it would have a magnetic field but acc. to a person on the ground it would just have an electric field. If there were a car moving relative to me , the person would...
  30. K

    Gravitational Field & Reference Frames

    In Newtonian physics gravity is a force and in relativity it's curved spacetime if I understand it correctly. So my question is, does the gravitational field of an object look different to different observers? What I mean is, does one reference frame see the strength of the field to be greater...
  31. L

    String theory and reference frames HELP

    I am reading The Elegant Universe...and I have bumped to possibly the first part of the book that I can not understand. When an electron and a positron pop out of existence, they soon annihilate each other with a "bang"...emitting a photon. If fundamental substance of universe are...
  32. A

    Special Relativity and reference frames

    Here's a statement that I'm supposed to solve: (\Deltax')2 = (\Deltax)2 - c2(\Deltat)2 And the accompanying text: "Show that (the equation above) is the same for all reference frames in special relativity" I consider myself somewhat decent with your basic special relativity calculations...
  33. M

    Oscillating table and reference frames

    Homework Statement A horizontal table oscillates with a displacement A sin ωt , where A = (Ax , 0, Az ) is the amplitude vector and ω the angular frequency in an inertial frame of reference with the z axis vertically upwards, normal to the table. A block sitting on the table has mass m and...
  34. C

    Special relativity inertial reference frames.

    [b]1. Suppose the space time co-ordinates of two events in inertial frame S are as follows: Event 1: x1=x0, t1=x0/c y1=z1=0 Event 2: x2=2x0, t2= x0/2c y2=z2=0 Show that there exists an inertial frame s' in which these events occur at the same time (i.e t1'=t2') and find the value of time...
  35. M

    Deriving acceleration in rotating reference frames

    Hi, everyone:) In my mechanics book a derivation is given for acceleration in rotating reference frames. However, there is one step I don't understand. First of all, it is derived that v=v'+\omega\times r' or \left( \frac{dr}{dt}\right) _{fixed}=\left( \frac{dr'}{dt}\right) _{rot}+\omega\times...
  36. B

    Inertial Reference Frames and Newtons laws

    Homework Statement I am a bit confused about what are inertial reference frames and what is not. The text states: "We define an inertial reference frame as a reference frame in which Newton's laws are valid... Accelerating reference frames are not inertial reference frames...
  37. P

    Special Relativity and Reference Frames

    Hi, I am a bit confused about a certain aspect of Special Relativity and I am hoping someone can clear this up for me. Let's say we have an event and two observers. Observer A stands a few meters from the event, Observer B is hundreds of thousands of miles from it. Relative to the event and...
  38. M

    Parallel conducting currents and the relevance of reference frames.

    i've just had this thing running through my head that I'm trying to resolve: 1. two parallel wires that conduct a current (same charge carriers) will attract one another, that is the magnetic force each wire emits due to the flowing current will induce an attractive force in the other (charge...
  39. M

    Understanding Reference Frames in Quantum Mechanics

    This might be a dumb question to ask, but does anyone ever worry about reference frames in QM? I'm just starting my first course and don't know much yet, but it seems like if we can consider operators to be vector fields (reference to my previous post) then we might have to worry about groups of...
  40. K

    Do Moving Reference Frames Affect Event Timing in Special Relativity?

    I picture two reference frames for two different objects moving relative to each other as two coordinate spaces S and S'. My question is, say both spaces start of on top of each other (ie both objects are initially stationary) and then the objects start moving relative to each other, would the...
  41. Q

    Work-Energy Theorem in Inertial Reference Frames

    OK, I'm working on a question regarding IRFs, but I seem to be a little confused. Question: Observer A is on the ground and Observer B in on a train moving with uniform velocity v wrt the ground. Each observes that a particle of mass m, initially at rest wrt the train, is acted upon by a...
  42. C

    On the noton of reference frames force and acceleration

    in the definition of inertial frame- a frame in which Newtons law of inertial holds- that a body will continue in its original motion unless impelled to change by a net force my problem is that, how do we know that a force is applied without acceleartion (ie only we conclude there is a force...
  43. F

    How can the Second Law of Motion be stated in a non-inertial reference frame?

    [SOLVED] Non-inertial Reference Frames Homework Statement State Newton's Second Law of motion in a non-inertial reference frame. Homework Equations In an inertial frame F=ma If S and S' are two reference frames, the same point is related by r=A(t)r'+b(t) where A is an orthogonal...
  44. S

    Interstellar space travel and reference frames

    Homework Statement A spacecraft with its astronaut has a total mass at rest of 10^5 kg. The astronaut is to travel to a star 10 light years away at a speed such that she only ages 1 year in her frame of reference a) the quantity 1-v/c where v is her speed with respect to Earth is? b)...
  45. R

    Q: Special Relativity: Moving Light w/ Mass & Reference Frames

    I have a very basic question about Special Relativity. I am very limited on my knowledge of physics and math and even more so on SR so please keep that in mind when answering. I have read the basic example many times of two spaceships traveling towards each other with a constant velocity. The...
  46. D

    True/False Help: Index of refraction and Reference Frames

    Which of the following statements are true? 1. The index of refraction is the ratio of the vacuum speed of light to the speed inside the medium. 2. The index of refraction is independent of the wavelength of the light. 3. If a light beam is incident perpendicular to the surface of another...
  47. gabee

    Velocities in rotating and inertial reference frames

    Can someone help clarify this equation from classical dynamics? It doesn't seem to make sense. Here's my textbook's explanation. A particle has position vector \vec{r} in a non-rotating, inertial reference frame (the 'un-prime' frame). Suppose we want to observe the motion of this object in...
  48. P

    Velocity of Raindrops: Car & Earth Reference Frames

    A car travels due east with a speed of 35.0 km/h. Raindrops are falling at a constant speed vertically with respect to the Earth. The traces of the rain on the side windows of the car make an angle of 65.0° with the vertical. Find the velocity of the rain with respect to the following reference...
  49. C

    What are the implications of rotational reference frames?

    It occurred to me that, as far as calculating the position or movement of objects a reference frame can be rotational, see the http://en.wikipedia.org/wiki/Rotating_reference_frame" . So instead of seeing the Earth as orbiting the sun you could say that the Earth is stationary and the rest of...
  50. N

    Understanding Reference Frames: Generality & Abstractions

    I am wondering about the generality of reference frames, and how abstract they can be. Is it possible for a vector in one reference frame to not exist in another frame? Or is there always a relation between two reference frames? Also, are two reference frames like two different sets of...
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