# What is Frame of reference: Definition and 203 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. ### Question about time dilation

My try which was failed : Observer at rest measures time ##\Delta {t'}= 2.2 \mu s## In the frame of reference of the Earth observer measures time ##\Delta t=\dfrac {\Delta {t'}}{\sqrt {1-u^2/c^2}}## I have two unknowns ##u## and ##\Delta t## so I cannot find ##u##. Is there another equation...
2. ### I Do electric currents depend on the frame of reference?

Suppose you have an infinite straight wire carrying electric current I. If you move in the direction of the electrons (opposite to the direction of the current) at the drift speed, would the current be zero in your new reference frame? Why or why not?
3. ### B What will be the ball's velocity after a perfectly elastic collision?

From the bus driver's point of view, who is at rest, the ball's initial velocity is ##u+v##. After the collision, its velocity has to have the same value, but an opposite direction, so ##-(u+v)##. So that means that relative to me standing on the ground at rest, the ball's new velocity is...
4. ### I Galilean relativity in terms of homogeneity

I have a question related to Landau's book. In that, he says: As an example, I'd like to bring a car and the ball hung inside the car and we can look at it from 2 different frames of reference. Frame of reference is me(I'm inside the car): If car moves with constant speed, nothing happens to...
5. ### B Length Contraction: Apple Hanging from Tree & Earth

Hello. Apologies, if this is already answered in other threads. Please redirect me, if that is the case. Imagine an apple hanging from a tree. Will there be length contraction between the apple and the earth in the frame of reference of the earth, as well as of the apple? All the best, Henrik
6. ### How much time do I have to catch a coin?

I am a bit confused with velocities in this problem. From Philipp's view, the coin's initial velocity is zero, so its transfer kinetic energy is also zero. When I am standing on a non-moving ground, is the coin's initial velocity ##v## in direction the walkway is moving? But won't I get then...
7. ### I Locally Inertial Frames: Freefall & Relative Velocities

When an object is in freefall, it is in a locally inertial frame of reference. If two objects are in freefall, can their locally inertial frames of reference have different relative velocities?
8. ### Square of orthogonal matrix vanishes

I found a the answer in a script from a couple years ago. It says the kinetic energy is $$T = \frac{1}{2} m (\dot{\vec{x}}^\prime)^2 = \frac{1}{2} m \left[ \dot{\vec{x}} + \vec{\omega} \times (\vec{a} + \vec{x}) \right]^2$$ However, it doesn't show the rotation matrix ##R##. This would imply...
9. ### B What is x' for Moving Rocket from P?

I have a rocket and it is moving straight from a point P with a velocity ##v##. When I say that ##x'=0## is at the place we sit in the rocket, then when the event happened outside his rocket at the point P, can I say that the coordinate of the event is for him negative, so ##x'=-vt'##, although...
10. ### 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?
11. ### Finding the position vector for translated frame of reference

what would be the y'-x' ##\vec r## vector be? I think it is ##\vec r = (8t - 1) \hat i + (6t - 2) \hat j## (not sure whether it is correct or not.) I thought about it as at t = 0 the position needs to be -1i -2j so that is why I took the signs in the y'-x' frame position vector as a - instead...
12. ### Classical Understanding Frames of Reference in Force and Motion: A Guide for 10+2 Students

I was starting out some problems on force and motion at 10+2 level. I was told you don’t need to know about frame of reference. But I want to. So which books are there to understand frames? Is it a part of relativity? If yes then which books? Thank you guys.
13. ### Finding the velocity of a car in a different frame of reference

Here's what I did so far. The velocity of the first car is ##v = v_0 +at## Frame of reference S = the road Frame of reference S' = the second car thus, v' is the speed of the first car in the frame of reference S' and v the speed in the frame of reference S. Here's what make me doubt. The...
14. ### 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...
15. ### 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...
16. ### 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...
17. ### B Inertial Frame of Ref & Forces: Understand Special Relativity

In trying to understand a bit of special relativity, I want to make sure if I understand it correctly, and I came up with the following question: "Imagine you would know all forces in the universe acting upon an object, doesn't that give away the only real existing frame of reference (imagining...
18. ### I Principle of relativity for proper accelerating frame of reference

Hi, I've a doubt about the application of the principle of relativity as follows. Assume as principle of relativity the following statement: It is impossible by any experiment performed inside a "closed" laboratory to say whether we are moving at constant velocity or staying at rest. Consider...
19. ### Restrictions on the frame of reference

Newton's laws only hold in intertial frames. In general, the center of mass (CM) is accelerating, so it cannot be used as a frame. However, 1. Suppose that CM is accelerating only in the ##\hat{z}## direction. Does this mean that the CM frame is still valid in the ##\hat{x}## and ##\hat{y}##...
20. ### 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...
21. ### Describe the length of an electron's journey in its own frame of reference

Lv = Lo / γ 1/γ =√(1-v^2/c^2) = √(1-0.8^2) = 0.6 Therefore Lv = Lo x 0.6 = 150 x 0.6 = 90m Therefore electron travels 90m in its own frame of reference (answer key solution) However, shouldn't the electron be assigned rest length, Lo, as its frame of reference is at rest with itself instead...
22. ### Frame of reference question: Car traveling at the equator

Earth rotate from west to east with 460m/s at equator. Car travel at equator from east to west at speed 460m/s. 1- What is car speed from inertial ref.frame? zero?How is zero if car travel in curved line? 2-What is car speed from rotational frame ? 3-How much is car weight,compare to car...
23. ### 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...
24. ### B Moving Faster Than Light: Are There Symmetrical Rules?

Would it be correct to say, that we are moving away from stars at the edge of the universe, at the same rate that these stars are moving away from us? I am relating to stars that are moving in relation to us, at a speed that is faster than the speed of light. Is the symmetry that maintains that...
25. ### I Special Relativity & No Special Inertial Frame of Reference

As per special theory of relativity, no inertial reference frame is special! If a spaceship is moving at 100 m/s, no one can conduct an experiment to determine whether it is moving at 100 m/s or the rest of the universe is moving to the opposite direction at -100 m/s, if I understand the...
26. ### Simple Canon Question (Conservation Of Momentum): Frame of Reference

Since Pi = Pf, 0 = MbVbg + McVcg I just need to express Vbg in terms of Vbc and Vcg (that is, I need to express the velocity of the ball relative to the ground in terms that I know/want to solve for): by reference frames: Vbc = Vbg + Vcg so Vbg = Vbc -Vcg Now I can sub in and solve 0 =...
27. ### 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...
28. E

### B Finding the length of a metre stick from a moving frame of reference

Suppose we have a stationary metre stick with one end positioned at the origin of a stationary frame of reference, pointing along the positive x axis. The world lines of both ends of the metre stick are consequently vertical. Now consider another primed frame moving at velocity v relative to...
29. ### Free fall time in an accelerating frame of reference

This is my wrong attempt, the bolt's equation for ##t\geq 2## would be ##y_b(t)=-\frac{1}{2}g(t-2)^2+e(2)+l## where ##e(t)=\frac{1}{2}wt^2## the position of the elevator's floor in the absolute frame of reference. ##d(t)=-\frac{1}{2}(w+g)t^2+2gt+2(w-g)+l## the distance between the bolt and the...
30. ### I The velocity of a moving frame of reference

In the attached fig 1 you have a moving frame of reference (MFR) moving in the direction V at velocity V Looking from above in the MFR there are 2 identical train carriages (car 1 and car 2), Car 1 is on a long set of tracks. Car 2 cannot move but is on train tracks. There are also 2 Identical...
31. ### Classical Book about center of mass frame of reference and fictitious force

Hello I have learned about conservation of momentum, Newton's law (1st, 2nd, 3rd law + free body diagram), conservation of energy and finding center of mass of several 2 D and 3 D shapes (non - calculus method). I watched youtube video about two objects connected by horizontal spring and in...
32. ### 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.
33. ### Moving charges in a moving frame of reference

Hi. If 2 bodies with charge q are in rest then both have electric force ##F_1=\frac{q*q*k_q}{|\vec{r}|^2}##. But in another frame of reference, that is moving with velocity v relative to first frame of reference, they feel both magnetic and electric force...
34. ### What is and some explamples of inertial frame of reference ?

I know this is a basic question, but I haven't understood deeply what a inertial frame of reference is, to be more specific, its relation with the first law of motion.
35. ### I The Expanding Universe and a stationary frame of reference

What is the rate of expansion of the universe and what is it's acceleration rate of expansion? Exactly? I recall it's about 67km/s at 1 mega parsecs? But then what's the acceleration rate? This exact information I cannot find. If the universe is expanding, and this expanding is accelerating...
36. ### B Special relativity - frame of reference

This must be a basic question. :) Bob and Alice have the same age. So in special relativity Bob leaves Alice and travels at very high speed and when it returns is younger than Alice. Bob's time is dilated and his space is contracted from Alice frame of reference. But now, if I take Bob's frame...
37. ### Forces in inertial and non-inertial frame of reference

Imagine such situation: A bus is moving at constant speed, a man is standing on the bus and is not holding to anything - he is simply standing. Now, the bus starts breaking with constant negative acceleration and so the man will change his relative position due to the force of inertia. Now...
38. ### Frame of reference/ time dilation

Homework Statement Imagine that you are flying on an airliner on a long flight to Europe, at a constant speed of 300 m/s. a) You throw a ball towards the back of the plane at 20 m/s. You then shine a beam of light towards the back of the plane. How will these two things-the ball and the...
39. M

### Why does kinetic energy depend on the frame of reference?

I'm having this discussion with my engineering peers: A ball is sitting on top of a train traveling at, say, 10m/s. The ball has mass of 2kg, for simplicity. The ball's kinetic energy KE relative to ground zero is 1/2 m v^2, or 100J. A person riding on the train picks up the ball and tosses...
40. F

### Frame of reference (non inertial/inertial) in an Atwood Mach

Homework Statement Find the acceleration of blocks 1 and 2 in both a non-inertial frame of reference (an observer accelerating with the machine) and an inertial frame of reference (observer at earth) Homework Equations F = ma The Attempt at a SolutionI solved the question successfully...
41. ### 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...
42. ### 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...
43. ### B Spin & Frame of Reference: Detecting Motion in Space

If we put a toy gyroscope in space, like the ones we all played with as kids with the wheel on the inside of a wire frame, and had nothing to reference it to. (stars, planets, dust, exc.) How could you tell if the inside was spinning or the wire frame??
44. ### I Big Bang timing: according to what frame of reference?

My apologies if there are some related discussions on this topic in another thread here, but I could not find one specifically addressing this question. Big bang theory, as it currently stands, talks of some extraordinarily precise time measurements; you see numbers like that 10^-37 sec...
45. ### B Which frame of reference is the correct one?

If everything is relative to something else, who's frame of reference is actually correct? For example an observer moving at 99.9%c will use the exact same laws of physics we use and determine without any doubt whatsoever that Earth is flat... flat as a pancake! So who's frame of reference is...
46. ### 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...
47. ### Why do two like currents attract (frame of reference)?

So the picture is this. Basically an application of amperes law and Newtons third law shows that they attract.But what about from the frame of reference of the moving currents. Say I have a stream of charges moving to the right, and another stream of charges moving to the right. Both with same...
48. ### 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...
49. ### B Function and change of frame of reference

Hello everybody, My question is about change of frame of reference and its consequences on an ordinary function. Let's ##B## a frame of reference that is linked to another one ##B'## through a change of basis matrix ##M##. So, for an equation written in the first basis ##B## as...
50. ### Universal stationary frame of reference for speed, d and t

So I understand this is probably more contiguous with philosophy than with physics, and there is probably no exact answer to this, but I had a couple of interesting questions relating to planes of reference, keep in mind I am a high school student and possesses very little knowledge of...