Reference Definition and 1000 Threads

Homework Statement A space traveler takes off from Earth and moves at speed 0.99c toward star Vega, which is 26.00 ly distant. How much time will have elapsed by Earth clocks when the traveler reaches Vega? 2. The attempt at a solution I looked at the problem solution, which...

In studying SR, I've been subscribing to a particular definition of a Frame of Reference that makes sense to me. Recently, I've been made aware by another PF member that there may be other, broader, definitions that are valid and that people use. I would like to know more about these broader...

Practicing Lorentz transformations but still not absolutely clear about conditions for observer's frame of reference. For example: Suppose that just as one of Einstein's long and surreally fast trains is passing a station platform, lightning strikes the platform at two points making scorch...

Hello I know that 5 volts in reference to ground (0 volts) is 5 volts as there is a potential differencce of 5 volts between 0 and 5 volts. Does this mean 5 volts in reference to 2 volts would be 7 volts as there is a potential difference of 5 volts between 2 and 7 volts? Thank you for...

Apologies in advance for the abstract nature of this question; I don't know enough about this field to be more detailed. I'm trying to understand the behavior of metal when heat is applied to it. I'd like to be able to answer such questions as: how fast does the metal melt? what is the effect on...

One can easily prove that \nabla \cdot f is invariant under a rotation of the reference frame, however I would like to prove that the divergence operator itself is invariant (same principle, different approach). In other words I want to prove that \mathbf \nabla = \mathbf e_x...

hey guys , is there anybody here to give me a nice reference for f(R) gavity ? Regards thecoop

I'm looking for an elementary book that has no prerequisites other than calculus, differential equations and elementary number theory about hypergeometric series. If it has good exercises in the end of each chapter, that would be great. Any suggestions would be appreciated.

Homework Statement I wanted to know if I consider the frame of reference as a rotating body itself, then will the points lying on the body rotating be stationary with respect to the rotating frame of reference? Homework Equations None The Attempt at a Solution As per me, if I am...

Hi there. I need help to work this out. A particle with mass m is studied over a rotating reference frame, which rotates along the OZ axis with angular velocity \dot\phi=\omega, directed along OZ. It is possible to prove that the potential (due to inertial forces) can be written as: V=\omega...

Basically: I jump forwards, exerting an amount of energy enough to push me forward with some velocity. But in my reference frame, I exert the same force, except the entire universe moves backwards with that same velocity, where did that energy come from? I sort of know this has to do with...

It is my understanding that the faster an object moves, the more energy is required to accelerate it. As an object approaches the speed of light, an infinite amount of energy is required to further accelerate it, which is why no object can travel faster than the speed of light. But movement is...

I have a question (thought experiment) that pertains to the speed of light and point of reference. I'm just interested in thinking about this subject and I can't quite get my head around this. I'm sure the answer is probably simple. Thank you for your help. By the way, if the answer involves...

I have a device (fNIRS, though knowledge of fNIRS probably isn't necessary to help) which produces very noisy signals and a noise reference. The noisy signal consists of a combination of a desired signal, and a noise signal, which is a scalar and phase shift of the noise reference. However, I'm...

Is there any other object except photon which moves at the speed of light? Why can't an object moving at the speed of light be taken as reference frame? Can we use the equation m=m(0)/sqrt(1-v^2/c^2) for an object moving with speed of light?

Homework Statement A spacecraft is in circular orbit around the earth. with respect to a point below it on earth, it is traveling towards the east with speed v. Specify the reference state for potential energy. Homework Equations The Attempt at a Solution the total...

Please suggest a good book which deals with the whole mathematical description of relativity (special theory as well as general theory, with tensor analysis). Also it would be much appreciated if the description was not very concise, as i am not an expert in the subject. Much Appreciated. :)

Hi guys. I am currently studying Sub-atomic physics and it seems to me that there are different formulas that work in different frame of reference. In particular, I would like to ask: 1. Which frame should we use in applying Fermi's Golden Rule? (I've read somewhere that the matrix element...

I have no background in relativity. Recently I started reading some introduction to special relativity in Griffith's EM book, where he vaguely defined an inertial reference frame as one in which Newton's first law holds. Now according to this definition, does such frame exist in nature? On...

Just saw this paper discussed (sort of) on Reddit, and wondered if it is old news. http://www.reddit.com/r/Physics/comments/tgvpn/a_rederivation_of_special_relativity_from_chaos/ (the URL is truncated so it gives the wrong impression ;)) I can't understand the maths behind it, but am very...

I would like to read more about this version of simplicial homology and cohomology. Any reference or explanation is welcome. I hope this description is correct. Triangulate a smooth manifold and assign an orientation to each simplex in the triangulation. Define the boundary operator...

Need help understanding inertial frames of reference! I'm doing an A2 physics unit on special relativity (AQA) and am really confused about this, but I only want to get the idea so don't go to deep please :) I understand that a frame of reference is an area which is fixed relative to...

Ok I'm really trying to understand inertial and non-inertial reference frames, my understanding is as follows: A rest observer on the earth, the observer will be stationary relative to the earth.. Now as I understand it an inertial reference frame is one of which 2 coordinate systems are both...

Homework Statement You are flying your personal rocketcraft at 0.9c from Star A toward Star B. The distance between the stars, in the stars' reference frame, is 1.0 ly. Both stars happen to explode simultaneously in your reference frame at the instant you are exactly halfway between them...

My question is not homework. I feel ashamed of having this doubts but I'm really stuck on this. The problem is I have a reference frame xyz and here I define the COM \vec x{_{cm}} of the system. Now I move the COM reference frame x'y'z': \vec{x'}=\vec{x}-\vec x{_{cm}} In this reference frame I...

Homework Statement Specify and explain whether the following is an inertial or non-inertial observer: An observer is placed on a rock between Andromeda and the Milky Way. Homework Equations N/a The Attempt at a Solution So here is my understanding, the observer would be situated...

Hi, Physics Forums! This is my first post here and I know just about zero physics, so I apologize in advance if the question is a little daft/naïve. Ok, so here's what I'm wondering: suppose you have a light source that produces EM waves in all directions at some frequency ν, and a camera set...

Hi there! I'm working on a couple of problems regarding simultaneity. For one I'm given events X_a = (ct,x,y,z) = (2,1,-3,2) and X_b = (6,3,-1,5) I want to find out if there's a frame of reference where the events are simultaneous. I find the change vector X_b - X_a = (Δct,Δx,Δy,Δz) =...

Homework Statement When the box is at the bottom of the incline it will have a velocity of vf The person is an inertial frame of reference with a velocity of vf When the person starts moving, the box is moving backwards with the velocity of vf. This means at the top of the hill the box has...

We know that we can't say whether we are at rest or uniformly moving if we're in a einstein cage..but if the same medium is accelerating/decelerating can we being inside(and can't see outside) claim abt state of cage..?I ve read that a non-inertial can be converted to inertial by incorporating a...

Hi, I have a couple of questions about velocities in inertial and rotating frames of reference, related by the following equation: \mathbf{v_i} \ \stackrel{\mathrm{def}}{=}\ \frac{d\mathbf{r}}{dt} = \left( \frac{d\mathbf{r}}{dt} \right)_{\mathrm{r}} + \boldsymbol\Omega \times...

Homework Statement The Millenia is catching up to the Galaxa at a rate of 0.55c when the captian of the Millenia decides its time to fire a missle. He uses a laser range finder to determine the distance to Galaxa and then he fires a missle that is moving at a speed of 0.45c. What...

Hi there, I am confused about the relationship between coordinate systems and reference frame in GR. I understand the coordinate systems can be used to describe reference frames, for example, Local inertial frames in GR can be defined by Riemann Normal Coordinates. However, take the...

The apparent path of an object is different for observers in different reference frames. A ball dropped from the top of the mast on a moving ship lands at the base of the mast. An observer on the ship sees the path as straight down while one on the dock sees the path as a diagonal. How many...

Last week I read this article in Science Daily about BOSS and its recent most accurate measurements of the universe to date. http://www.sciencedaily.com/releases/2012/03/120330081844.htm In describing the experiment to measuring the accelerating expansion of the universe...

A charged particle is placed next to a current-carrying wire. The wire produces a magnetic field, but if the particle is at rest, the field exerts no force on it. However, in a different inertial reference frame moving at speed v parallel to the wire, the particle is seen to be in motion, and so...

Homework Statement The distance from Planet X to a nearby star is 12 Light-Years (a light year is the distance light travels in 1 year as measured in the rest frame of Planet X). (A) How fast must a spaceship travel from Planet X to the star in order to reach the star in 7 years...

I have just completed my class 10th. I was presently reading the class 11th H.C Verma physics textbook and here is what I confronted which seems to me as if I am unable to fathom : Now I can't understand that how come acceleration of book with respect to Earth isn't 0 ?! Please see bold part...

Hi, This is partly inspired by the questions in the thread about normal forces on a cornering car but I thought I'd post here instead of mix that thread up with my question. So suppose we have a biker leaning into a corner. There are the normal force and the force of friction which act at the...

Hey guys girls and thanks in advance (Sorry if this post is in the wrong area) Ive been working with splines in 2D for a little while now and am fluent with the mathematics behind them. I now need to use 3D splines but cannot come across a good reference material to reconstruct them ...

In voltage divider, how high must the resistance on Vout be so that voltage divider can be used according to convention? I'm looking for official references.. If anyone can help I'd appreciate it.

quantum optics is a reference to a "c-number" Hi In my lecture notes on quantum optics is a reference to a "c-number" electric field, and it is stated that, since it is a c-number, there is no corresponding Hamiltonian. As far as I have understood, a c-number is a classical value of some...

Hello All, The following may be a simple problem. But, your thoughts will be very much appreciated. Homework Statement Let's use a gun with mass m1 and a bullet m2. The bullet is fired in the positive direction with speed v2, and the gun recoils in the negative direction with speed v1...

If we have light, any particle, and maybe car, the particles travel at 0.98c and car let say 50m/s. Let them start moving at the same time to the given point let say 300 metres away. The difference between times of arrival of light and particle will be small compared to that between light and...

Hi, Anybody used TI's SN74LV132 'NAND Gate with schmitt trigger i/p' in their design or any other similar part ? If so, please send me any Reference schematics or application notes.

Hey guys, I am having some problems with the concept of inertial/non-inertial frames of reference and their applications in engineering dynamics. So I've learned that a given frame of reference is defined to be non-inertial when something in the studied system can only be explained through...

Homework Statement A 20g ball of clay is shot to the right at 12m/s toward a 40g ball of clay at rest. The two balls of clay collide and stick together. Call this reference frame S. Homework Equations What is the velocity of a reference frame S' in which the total momentum is zero...

This thought experiment involves two people named Person-A and Person-B. Person-A fires a gun from a car which is traveling at 60mph. Imagine that the bullet travels at a constant speed of 300mph for some time, assuming that the air friction is ignored. Person-B is stationary observing the...

Hello, I am having difficulty understanding the concept of Newton's first law only applying in an inertial reference frame, or a frame that is at constant velocity, however, apparently the 1st law no longer applies if the reference frame is accelerating. Can anyone give me some sort of concrete...

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