# Frame of reference Definition and 28 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. ### Can two objects moving parallel relative to a ground meet?

I think that yes but how to explain it when someone standing on a ground sees them moving paralell? If I move properly, I can see two cars moving paralell ralative to the ground crashing, while someone on the ground do not see them crashing. Is it consistent?
2. ### I Is acceleration a more absolute/fundamental quantity in the universe?

Was wondering if acceleration seems to be a more fundamental property/quantity in the universe as compared to velocity or distance because acceleration can be defined in more absolute terms in a frame depending on the forces acting inside that reference frame. Considering a very simple example...
3. ### I About global inertial frames in GR

Hi, starting from this thread Principle of relativity for proper accelerating frame of reference I'm convincing myself of some misunderstanding about what a global inertial frame should actually be. In GR we take as definition of inertial frame (aka inertial coordinate system or inertial...
4. ### I GPS clock synchronization in ECI frame

Hi, starting from this old thread GPS clock synchronization I've a doubt about the physical process employed to synchronize clocks bolted on GPS system satellites. We said that clock synchronization is frame dependent. In other words we must select a coordinate chart (aka reference frame) that...
5. ### Momentum in different referance frames

I aready got the solution for this exercise. However, the solution used the referance frame from the car: What I'm trying to understand is the line: Because before reading the solution, I was trying to solve it using the lab frame. So this is my work so far: Using conservation of momentum and...
6. ### I About inertial reference frames and logical deduction

Hi, consider the following in the context of classic mechanics and SR. We know there exist special "frame of reference" according to free objects stay at rest or keep moving with constant uniform velocities. Suppose you single out a such reference frame according to the Newton law of inertia...
7. ### B Can entangled particle pairs be measured at the same time?

Has there been an experiment where 2 particles that are entangled are measured at the same time? If so what was the result? Can any observer occupy the same frame of reference down to an electron? Don't we all exist at different times based on our frame of reference so none of us can share the...
8. ### What forces affect an astronaut?

Well the first one that comes to mind is gravity and maybe centrifugal/centripetal force. I imagine that forces such as drag shouldn't even be considered. I find it difficult to imagine which belong to which frame of reference.
9. ### Force in Center of Mass frame equaling zero

Homework Statement Suppose I have particles with masses m1 and m2 , both are in freefall: Then , looking at the center of mass coordinates , I know that the sum of momentums of masses m1 and m2 in the center of mass coordinates is equal to zero : P1c + P2c = 0 so now I know that the total...
10. ### Particle defined "at rest" compared to a magnetic field?

I am trying to understanding magnetism and I've been running into this thought problem A particle a in a magnetic field B responds with Force F=|q|v x B. frame S: The field is B1, caused by a moving charge/s - current at speed v. the particle is at rest, F=0. frame S' moves with speed v/2...
11. ### I Special relativity: frames of reference

Hi people, I have a question about the frame of references. Let's have an example: First case: Jill on rocket and Jack stationary on Earth. Jill moves relatives to Jack 0.6c (1.8*10^8m/s). The distance is 18*10^8m. At the zero time Jack and Jill synchronize their clocks. Then Jill starts to...
12. ### B RC Helicopter in a Train (Forces)

I was talking to my Physics teacher about this at lunch. If I was to have an rc Helicopter which i had hovering perfecting (if only i had the skill) on a train at rest. What would happen in terms of the position of the helicopter as the train accelerated? Would is stay at the same point in...

Definitions: Astronaut is A Person on Earth is B A travels to a star far away at near light speed, A would see B's time dilate. B would also see A's time dilate Twin paradox revived: What would happen if A returns to B at a very slow speed? Then both frames of reference would see each others'...
14. ### I Galilean transformation paradox help

I'm getting quite stuck on this problem here. Galileo said that Xb = Xa - V*Ta. (This follows from dv = dx/t --> Xa - Xb = t*dv --> the above formula) Thus, it is concluded Xa = Xb + V*Ta, but why? In my thought experiment the objects are moving relative to each other, thus if A is moving away...
15. ### I How is motion in space different than motion in spacetime?

If two particles are moving apart, how is it determined if they are moving through space or if the motion is due to the expansion of space-time? Especially if there was no other frame of reference.
16. ### B Where is the slowest point in terms of time?

If moving inside the event horizon of a super-massive black hole and theoretically surviving we could see the universe pass by at millions of years per second relative to someone on earth, where could we go where time passes at a much faster rate than someone on earth? For example where 2...
17. P

### What's the difference between an inertial frame....

And a cartesian axis system in physics? I thought about that and my answer is that a cartesian axis system is the same as a inertial frame of reference, is that true?
18. ### Is "inertial frame of reference" the same as spacetime?

Is the inertial frame of reference the same thing as space time?
19. ### Changing the frame of reference

I'm currently doing a student project at uni and I'm trying to design magnetorquers for cubesats.Before I make the prototype I need a simulation of what will happen.The problem is that for my calculations,I need to change the frame of reference of the geomagnetic field.So basically I need to go...
20. ### Coordinate transformation - NED and ECEF frames

Hi, I have a reference device that outputs euler angles, which are angles that relate the sensor body frame to the north east down frame. These angles are called pitch roll and yaw. The sensor is an accelerometer. I know how to get the rotation matrix that will put accelerations from the...
21. ### Frames of reference and vectors problem

Homework Statement A car is moving toward north with a speed of 35 km/h. A truck travels toward west with a speed of 42 km/h. Which is the speed of the caravan according to the car's driver? Homework Equations The Attempt at a Solution The solution given by the book is 15 m/s with direction...
22. ### Universe frame of reference

Dear PF Forum, Sorry if I ask again, because I want a detailed information. Does the universe has a frame of reference? Two twins. A stays, B "travels". (Travel here is confusing, B will say I stay and A travels) and B "turns around" and come back. B ages more slowly then A. Q1: Why? A1...
23. ### Frame of reference and the varying mass problem

Hi Friends , I had a discussion with a funny person last night. He said the following argument : Suppose there are 21 objects including the one object under consideration. Each of the 21 objects move with a velocity. Since there are 21 objects, for the object we are considering has 21...
24. ### Universe frame of reference

Dear PF Forum, Again the same question about preferred frame of reference. I have read several threads in Physics forum, but I think this question belong to cosmology. And I have searched in Google and in PF forum threads, so, I'll ask some confirmation here. 1. Does the universe have a...
25. ### Rigidly Constantly Accelerating Frame

We know that when a rigid frame, say a rocket undergoes constant proper acceleration, its worldline is hyperbolic. The equation is given by: x^2 - c^2t^2 = \left( \frac{c^2}{a_0} \right)^2 Suppose P is such a worldline and worldine can also be written as: I understand how these are...
26. ### Frame of reference and Pseudo forces

If you have a car and a pendulum is hanged inside it, and if you watch from outside the car,and if the car has some acceleration, then you see the bob moving in opposite direction of motion of car. For a person standing outside, he knows that the car has some acceleration. What causes the bob...
27. ### 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...
28. ### Question from "Introduction to Tensor Calculus, Relativity" about Frame of Reference

I already have the solutions emailed to me from a D H Lawden textbook. I have trouble understanding the solution as the solution is not formatted properly, and the answer seems to be a little too advanced for me. I hope that some one can help me understand the problem. 1. Homework Statement...