A system of coordinates used as the basis for describing the position and motion of objects

learn more… | top users | synonyms

4
votes
1answer
373 views

Relativity of simultaneity - An example

I am trying to understand the relativity of simultaneity in different frames, and I am trying to work out an example. Suppose along the x-axis there are two points 2000m apart. Event A happens at t=0 ...
4
votes
2answers
142 views

Effect of gravity at near-lightspeeds

Let's say I'm in a space station, hurtling towards our galaxy nearly close to the speed of light. From my reference frame, I see the galaxy coming towards my ship at the same speed. I pass the Sun, ...
4
votes
1answer
128 views

Pseudo Force Other Than Centrifugal Force In A Rotating Frame

I read in HC Verma that if we are observing the motion of a body from a rotating frame and the body under the observation is NOT in motion with respect to our frame than centrifugal force is the ...
4
votes
0answers
94 views

Principle of relativity - a second, equivalent form, using invariants

Most people state the principle of relativity like this: "The rules of physics must take the same form in all inertial frames." Question: is this an equivalent way of saying the same thing: ...
4
votes
0answers
834 views

Difference between Eulerian and Lagrangian formulation of Fluid Dynamics

Difference between Eulerian and Lagrangian formulation of Fluid Dynamics. I am completely new to fluid mechanics. Until now definition $F = ma$ was sufficient for me to solve any rigid body problems ...
4
votes
1answer
158 views

Is it possible to have uniform proper acceleration along a large object without breaking it?

I'm learning about accelerating reference frames (to eventually get grasp of general relativity too). I've just read about the Rindler coordinates and this one caught my eye Note that Rindler ...
4
votes
0answers
231 views

Tensor equations in General Relativity

In the context of general relativity it is often stated that one of the main purposes of tensors is that of making equations frame-independent. Question: why is this true? I'm looking for a ...
3
votes
4answers
505 views

Why are people weightless whilst in orbit around the Earth? ISS? Satellites? [duplicate]

Had physics for 2 years now on highschool, but there is a thing I am wondering about. You know the in the height above the earth surface around where the satellites are (Or the ISS), I've calculated ...
3
votes
2answers
160 views

Twin Paradox in case of two twins that don't meet

If there are two twins. such that one of them goes on a space voyage maintaining a constant velocity, and that one never returns to earth, and the twins decide to never meet but send information about ...
3
votes
3answers
459 views

Centrifugal Force

When a body is in circular motion, realistically, it experiences only the centripetal force, created by gravitational pull, tension etc. , which gives it acceleration towards the centre. Now, assuming ...
3
votes
3answers
273 views

First Postulate of Special Relativity: What does it mean?

Wikipedia has this quote: Special principle of relativity: If a system of coordinates K is chosen so that, in relation to it, physical laws hold good in their simplest form, the same laws hold ...
3
votes
1answer
277 views

Is a preferred reference frame of the universe the old aether?

About two years ago I posted a question about a symmetrical twin paradox: Here. Recently a new answer was posted and an intense discussion ensued: Here. One of the points discussed concerns a ...
3
votes
1answer
163 views

Angular momentum depends on origin?

The angular momentum of a particle rotating about a point is given by $\vec{L} = \vec{r} \times \vec{p}$. Imagine a particle tracing a circular path on a flat table. If I put the origin of my ...
3
votes
2answers
344 views

If I travel close to the speed of light and come back, why is everyone else dead, and not me? [duplicate]

Consider the following scenario: I get in a spaceship, and travel really close to the speed of light for a while, and then come back. A lot of time has passed on the Earth, but since I was traveling ...
3
votes
3answers
1k views

What provides the centrifugal force for planets orbiting a star?

this is a question I had when I was a kid. I'm a bit ashamed because I think I am missing out on something very obvious since I have the same question despite almost being an engineer now! From ...
3
votes
4answers
267 views

What does 99.9% speed of light mean when there is no absolute velocity?

So when people say: 'I am approaching the speed of light, and to get to 100% light I would need infinite energy' they are essentially saying that this situation is impossible? I read this in ...
3
votes
1answer
100 views

Paradox of angular velocity

For a torque-free symmetric top, the Inertia tensor has an inverse $I^{-1}$, and $L=I\omega$. Which implies that $\omega=I^{-1}L$. But since $I, L$ are constants, $\vec\omega$ is a constant. However, ...
3
votes
2answers
66 views

The speed of light as it approaches a massive body

No matter how fast you go, you will aways perceive the speed of light as constant. Taking that as a fact, the special relativity theory was formulated. Now, for what I understand about general ...
3
votes
2answers
121 views

Time Slowing Down [duplicate]

I'd like to ask a question if I may about the relativity. When travelling at the speed of light(which is impossible for particles with masses) or very close to it, would it be me, myself, seeing my ...
3
votes
1answer
313 views

Reference frame involved in the Schrödinger's equation

I have a doubt as to in which frame of reference the Schrödinger equation is written? I think it is inertial but can't reason it out.
3
votes
7answers
435 views

Relation between coordinates and frames of reference

I always get a little uneasy that all the theories I can think of (at least since Newton) are constructed in a way such that they would be true in heaven and on earth ... but we can never go ...
3
votes
4answers
707 views

How fictitious are fictitious forces?

How fictitious are fictitious forces? More specifically, in a rotating reference frame i.e. on the surface of the earth does an object that is 'stationary' and in contract with the ground feel ...
3
votes
3answers
173 views

Conical vs Simple Pendulum

I don't understand why the Tension $T$ on a conical pendulum and a simple pendulum are different. In a simple pendulum, one would say that the tension of the rope is $T=mg \cos(\theta)$. However, ...
3
votes
2answers
88 views

Is a particular force different in different frames

Can a particular real force have different magnitude in different frames?
3
votes
1answer
180 views

Space time a function of itself, objects in it, or both?

Is spacetime a function of itself, objects within it, or both? I am struggling to understand just what is spacetime without objects in it (or theoretical reference points) and thus no frame of ...
3
votes
1answer
244 views

Why can we use just one angular velocity vector to describe the rotation of a whole non-inertial reference frame?

The other day in class the professor was explaining non-inertial reference frames. We were working out how to find the acceleration of a point as measured from the non-inertial reference frame, and ...
3
votes
1answer
71 views

Is there a technical term for “meaningfulness” of mathematical operations?

Is there a technical term for "meaningfulness" of mathematical operations? For example, adding vectors that represent forces has a meaning regardless of the coordinate frame, but an elementwise ...
3
votes
1answer
57 views

Why is it that angular acceleration is constant in different instantaneous reference frames?

Take the following example: A rod (of length L and mass m) is held horizontally at both ends by supports. One is instantaneously removed. The specific problem is to prove that the force on the other ...
3
votes
1answer
99 views

Can a simulated Universe simulate Special Relativity

I know there are theories (or postulates) that hold that our Universe could be a simulation. I was wondering, if Special Relativity states that two events which are not causally linked can be judged ...
3
votes
1answer
65 views

Primary direction in planet-centered equatorial reference frame

I am given the classical orbital elements of the orbit of a spacecraft around a planet which is not the Earth, say Venus. I assume those are referred to a reference frame whose fundamental plane is ...
3
votes
1answer
71 views

Do particles keep on emitting energy?

Accelerated electrons emit electromagnetic waves, but those at rest do not. So accelerated electrons emit energy and those at rest do not. (At rest hypothetically, I know it is not permissible ...
3
votes
3answers
193 views

Speed of light travel

I have just started special theory of relativity. The limiting speed known as speed of light fascinated me most. I asked my teacher: Consider two massless objects moving in the same direction at ...
3
votes
0answers
68 views

Why rendezvous attempt failed on Gemini 4?

It is said in Wikipedia, that On the first orbit, McDivitt attempted to rendezvous with the spent Titan second stage. This was unsuccessful for a number of reasons: NASA engineers had not ...
3
votes
1answer
164 views

Finding frame of reference where angular momentum appears zero

Consider a isolated system of $n$ non-interacting classical particles. We can easily select a barycentric frame of reference, where total momentum will be zero, so we have our $\vec x(i)$ — ...
3
votes
3answers
231 views

Frame of reference and big bang

I have read Brief History of Time in which he has wonderfully described the formation of universe. What is the frame of reference from which we are viewing the big bang? What is the frame of reference ...
2
votes
6answers
600 views

Does the (relativistic) mass change? Why?

I learned recently that when an object moves with a velocity comparable to the velocity of light the (relativistic) mass changes. How does this alteration take place?
2
votes
2answers
270 views

A relative time dilation paradox.

Let us assume that there are two astronauts A and B who are floating in space. A sees B passing by and vice versa. A sends signals to B every minute. According to A since B is moving his clock will be ...
2
votes
3answers
272 views

If time slows down when you move faster, does this give you an “effective speed” different from your proper speed?

Suppose you're travelling at 0.9c toward the sun, and you tag past the Earth and start a clock. Would Lorentz contraction/time dilation cause you to get to the sun faster than (about) 9 minutes ...
2
votes
4answers
74 views

Sum of acceleration vectors

If a point mass has some accelerations $\mathbf{a_1} $ and $\mathbf{a_2} $, why is mathematically true that the "total" acceleration is $\mathbf{a}= \mathbf {a_1}+\mathbf {a_2}$?
2
votes
2answers
140 views

Light in Different Reference Frames

I think I'm just confused, but for some reason I thought that light moving straight in one frame would have to move in the same direction in another frame. I know there are photons-but because I have ...
2
votes
2answers
99 views

Terminology for opposite null lines

Is there a name for two null lines that lie on the opposite sides of the null cone? Each line can be obtained from the other by reflection in the axis of the null cone (the time-axis). In terms of ...
2
votes
2answers
60 views

Is speed of light ( Sun-to-Earth ) related to the movement speed of solar system?

The speed of light has been measured to be 299 792 458 m/s. Now, the Solar System is traveling at an average speed of 828,000 km/h (230 000 m/s). Summing up the numbers we get close to 300 000 000 m/s ...
2
votes
4answers
87 views

Special Relativity moving in space

Given that time is 'just another' dimension and people get hung up on the fact that we cannot go back and forth in time like the other dimensions. Is there any proof that the corner of 8th Avenue and ...
2
votes
2answers
112 views

Increase in Mass with Velocity [duplicate]

I just had a confusion. Does the mass of the body actually increase when it is moving with a certain velocity? Or does it only look like the mass has increase to another observer. How can the actual ...
2
votes
1answer
206 views

Can we live forever by taking advantage of the time dilation effect?

I have been reading about Time dilation and twin paradox in Relativity. So,I thought that if It can be the difference of 10 yrs between the Girl in space and on Earth, then why can't anyone not age ...
2
votes
1answer
276 views

Thought experiment about acceleration

Case 1: two people wake up in spaceships accelerating at 1g. They can measure or observe anything inside the room but not outside. They couldn't determine if they were on a spaceship or on earth. ...
2
votes
2answers
172 views

What is wrong with considering the Atwood machine as a system?

I am confused about a method used in the following problem. There is an arrangement as shown below. The surface is smooth, and the pulleys are light. We have to find the acceleration $a_0$ of $m_1$. ...
2
votes
2answers
172 views

How long does it take for a black hole to form?

The well-known fable of an astronaut sending signals out to an external observer while falling toward an event horizon states that the time lapse between such signals becomes greater even if in the ...
2
votes
2answers
160 views

Centripetal force in frame of reference of body moving In a circle

Suppose a body is moving in a circle about a fixed point. In the frame of reference of the body, is the centripetal force felt or is only the centrifugal force felt? More generally, does a body only ...
2
votes
4answers
770 views

pendulum is a inertial frame of reference or non inertial frame of reference? [closed]

Example of pendulum is inertial frame of reference or non inertial frame of reference? because if pendulum starts moving its continuously moves without changing there period of time but is changes its ...