Reference Definition and 1000 Threads

From the basic definition of vacuum energy as being tied in with the Uncertainty principle, I would expect this not to include the Cosmic Background Radiation. Right? On the other hand, in figuring out (a) the Casimir effect, one attributes the force to the field between the plates carrying...

Hi there, I have been searching multiple websites and forums but have not found a cohesive answer to my queries. I am currently going through this textbook to learn pre-algebra: https://www.amazon.com/dp/0618250034/?tag=pfamazon01-20 Also, is this a good book to be studying as an autodidact...

Hi, a very basic question: what is a good intuitive way to understand the importance of a reference prior? In the context of a signal search. Bellow, I also try to give the way I understand the approach in a Bayesian analysis (roughly): 1. You have your likelihood model L = p(x_{obs} | \lambda...

Homework Statement In my reference frame, I see two carts collide. Both cart A and Cart B have a mass of 2 kg. Cart A has initial velocity v= 3 m/s i-hat + 2 m/s j-hat, cart B has initial velocity v= 3 m/s I-hat + 4 m/s j-hat. 12 J are released in the collision. In previous parts of this...

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...

Hi everyone, I am trying to get familiar with some of the terminology and concepts recurring more or less everywhere in LHC phenomenology. In particular, something that is troubling me a bit is the concept of sudakov form factors, which I don’t find explained anywhere in an understandable way...

To what extent is the Heisenburg Uncertainty principle a statement about moving frames of reference? The ill-defined position of a particle seems to imply that one can never find an inertial frame of reference in which the velocity of a given particle is constant.

Consider a specific reference frame (0XYZ) attached to Earth. A point (origin) being selected, coordinates are ascribed along with a vector basis. This reference is non-inertial because it is locked to Earth and the acceleration of Earth is not zero. Suppose upon rising one morning I felt...

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...

Homework Statement I'm using Shankar's Introductory Physics course and I can't get a question out of my head regarding his setup of Relativity. There are two observers, S and S'. Observer S is stationary, while Observer S' is sliding past S (to the right) with velocity u. They agree to set...

I'm building an Arduino voltage logger that includes an op-amp (OP27G) as a buffer on the input. Since I'd like to be able to measure voltages all the way down to zero, I want to power the amp with a bipolar supply. My initial thought was to build the rail-splitter below so I wouldn't have to...

This Wikipedia article https://en.m.wikipedia.org/wiki/Relativistic_electromagnetism seems (to me) imply that there is always a frame of reference in which a magnetic field can be rather viewed as an electric field modified by relativistic considerations. Is that always true? That is...

Hi, Could someone please have a look at my solution and let me know if I did it correctly. Thank you! 1. Homework Statement A pilot is flying from City A to City B which is 300 km [NW]. If the plane will encounter a constant wind of 80 km/h from the north and the schedule insists that he...

Homework Statement Special relativity: A rod traveling with the relativistic velocity of 0.866c moving towards a garage. The length of the rod is L, that of the garage is L/2. From the reference frame of the garage, we find the value of Lorentz factor = 2 we say that rod would fit inside garage...

Homework Statement A child stands near the middle of a roundabout that is rotating with some angular velocity w. The child moves towards the edge of the roundabout in a straight line from the child's perspective and at constant speed. Explain in as much detail as you can (and using equations)...

Suppose I'm an observer out in space and 30 km from me there's another observer, who is static with respect to me. Let's say my name is A and the other is B. We're both far far away from all the cosmical objects that might have a gravitational influence on us. We both notice a spaceship flying...

I'm attempting to use an algorithm translated from Jean Meeus: Astronomical Algorithms. The algorithm in question finds a geocentric position of the moon given a certain day. I have been able to find the geocentric longitude of the moon, but I don't know what this longitude is in reference to...

I study electromagnetism and I got to the chapter about special relativity, in this chapter my professor (since we are not using the electromagnetic tensor in this course) used a specific case to show that the electric field parallel to the velocity of a frame of reference stay the same in both...

So there are no "absolutely motionless" reference frames, but is there a set of reference frames which could be described as "absolutely rotation-less"?

Reference point was chosen to be at Va. I'm trying to understand the logic behind it. It is clear that Vc = - Vs because if Vc was the reference point at Va the voltage potential between Va and the reference point Vc is Vs. Therefore, Va = Vs, Va - Vc = Vs if Vc is reference. However, when Vc...

Homework Statement I know that potential gravitational energy is relative to the reference point that I decide to choose (like in the picture below). But then if, for instance, I set my reference point in the ceiling and my vertically down y-axis to be positive. What would the potential...

Speed of a wave in a string is given by √(τ/μ) . But this speed is with respect to which reference frame? Since, the speed depends on τ and μ( which are independent of reference frame ), I can consider speed of wave independent of reference frame. But this is not so. From experiment, we know...

Person A is in car A and person B is in car B. These people don't know if their car is moving (i.e. there is no scenery and their engines don't vibrate or make noises). Car A is stopped and car B is moving with a velocity v. Person A thinks that car B is moving with a velocity v while person B...

In the wave equation## \frac {\partial^2 \psi} {\partial x^2}=\frac{1}{v^2}\frac{\partial^2 \psi}{\partial t^2}\tag{1}##, v is the speed of the wave propagation. With respect to which reference frame is this speed measured( in general)?

Hello everyone. Below are two problems I have been thinking about lately. Let’s consider two cases: we have a spaceship surronded by an utter void - nothing outside which the spaceship’s pilot could refer to. The pilot (in his robotic body, allowing him to withstand enormous G-forces) turns on...

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??

In the book General Relativity for Mathematicians by Sachs and Wu, an observer is defined as a timelike future pointing worldline and a reference frame is defined as a timelike, future pointing vector field Z. In that sense a reference frame is a collection of observers, since its integral lines...

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...

I am amused by how skillfully most of the texts I have avoid discussing reference electrodes in electro-chemical measurement-They simply start out by discussing the H2 and Calomel electrodes with no further explanation. Both have certain hazards and seem overly complicated. So--why are these...

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...

Special relativity states that the speed of light is constant for all the references, as long as they are not accelerating. For example, the speed of light would be c for a train moving linearly with a constant speed and would also be c for an observer who's not moving at all (I took the Earth...

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...

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...

When analyzing the conservation of angular momentum of a particular system, should we use the same p.o.r. before and after or can we use different p.o.r.'s? As far as I know, we should always use the same reference, but sometimes I see several solutions that use different references in my...

Hi all, I have a little problem while reading Feynman lecture note volume 2, chapter 40, section 40-3. In that section Mr Feynman talked about Bernoulli equation and a example of a filled water container. In high school we learned that if we drill a hole near bottom of container, we can get...

Hey everyone, I'm in my second semester of programming which covers an introduction to C++ (the prior course was Python). We just covered classes and arrays, and are moving onto intro. to algorithms and pointers (we're currently mid-semester). In the algorithms chapter, they covered 4 "basic"...

Homework Statement Let ## \mathbf{r} ## be the position of a point in a rigid body relative to some origin ##O##. Let ##\mathbf{R}## be the position of the centre of mass from that origin. ##\mathbf{r^{*}} = (\mathbf{r}-\mathbf{R})##. ## d\boldsymbol{\phi} ## is the infitesimal vector directed...

Homework Statement Observer O at the origin of a coordinate system is at rest relative to two equidistant space stations located at x=+3.00×10^6km (station A) and x=−3.00×10^6km (station B) on the x axis. In reference frame O, station A sends out a light pulse at t = 0 (event 1) and station B...

kuruman submitted a new PF Insights post Frames of Reference: Linear Acceleration View Continue reading the Original PF Insights Post.

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...

Ok I have a really basic question. Say you and I are floating in space and there is a single electron in front of us stationary to our frame of reference. Now I start hopping up and down. I see the electron accelerate up and down from my hopping frame of reference. I see a EM wave be...

Hello forum members, The electric potential for a point charge is a scalar function given by $$V = \frac {kq}{r}$$ This means that the potential has a nonzero value everywhere. The potential becomes ##V=0## when ##r=\infty##. However we know that what matters is the potential difference...

I work part time at my school. I just asked to change my schedule at work because it was affecting my school stuff, and my boss kinda freaked out. He is the type that takes things very personally and was extremely offended when I requested to change my schedule. I have been a very good employee...

I was watching one of the documentaries of Brian Greene (Beyond Cosmos). here at (12:00-12:10) he says.The skater spins respect to space. My question is How can space-time can be a referance frame itself ? Is it means we can just pick a coordinate and make it a referance frame ? (Sounds...

Homework Statement Sonia walks up an escalator which is going up. When she walks at one step per second, it takes her 20 steps to get to the top. If she walks at two steps per second, it takes her 32 steps to get to the top. She never skips over any steps. How many steps does the escalator...

Homework Statement You are standing at x = 9.0 km and your assistant is standing at x = 3.0 km. Lightning bolt 1 strikes at x = 0 and lighting Bolt #2 strikes at x = 12.0 km. You see the flash from Bolt #2 at t = 10 μs and the flash from Bolt #1 at t = 50 μs. According to your assistant, were...

Uniformly accelerated reference frames in special relativity are represented in the space-like region of a lightcone as hyperbolae. These hyperbolae represent worldline of accelerated observers. However, there could not be be causal relationship between two events on the spacelike section...

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...

What determines whether a frame of reference can be considered stationary? I assume it is not allowed that the Earth be considered stationary and the universe is moving around it for example, as I would have thought that would lead to observation of faster than light movement. In...

Some time in the 1980s when I first started studying relativistic gravity, for ease of comparison with Newtonian and Special Relativity gravity I worked through pages of geodesic equations for a general isotropic coordinate system with spherical symmetry, converting everything to terms relating...