Reference Definition and 1000 Threads

I apologize if this has been asked before. I searched numerous times and couldn't find any discussion on this specific topic. Every description I've read of the impossibility of FTL signaling uses some variation of this diagram: http://www.theculture.org/rich/sharpblue/archives/000089.html...

Consider I am in the train with a ball traveling at normal speed of a train. I drop the ball, it follows a straight path of descent and falls in front of my feet. For an observer on the platform, the ball follows a parabolic path and falls in front of my feet. (Please go to this...

I was just working on my knowledge of the twin paradox, and had a question that I couldn't find an answer to anywhere: If I understand it correctly the paradox is resolved because the two frames are not symmetrical, one is non-inertial, so that frame has it's clock run slower. So if you carry...

I'm looking for a list of "natural" frames of reference on the cosmic scale. Something that can be used as "the" frame of reference for everyone in the universe that isn't arbitrary. So let's brainstorm about some potential candidates. The more the better. If need be, start with an idea and...

I am a bit confused by the equations for Fdrag (the force drag applies to an object) and Pdrag (the power required to overcome drag). F_{drag} = \frac{1}{2} C_{d} \times \rho \times A \times \nu^{2} Where: C_{d} is the Drag Coeffecient (a dimensionless, empirically-derived constant)...

I understand the Michelson–Morley experiment and its result; but what I don't know yet is the REASON. Example: A torch in free space is moving at a velocity [v] w.r.t me. Considering the material nature of light, shouldn't the speed of photons emitted from the torch be [v+c] w.r.t ME? According...

Homework Statement A child sits 2m from the centre of a merry-go-round (a rotating wooden platform) which is rotating at 3.5revs/min in a clockwise direction (when viewed from above). She places a wooden block of mass m=0.25kg beside her on the platform. a)Draw a diagram showing all the...

Does anyone know of a good link to basic transformer design? I keep seeing the standard equations but they don't seem like much help. I can't seem to find any good guides for designing the most basic transformer For example, I will see equations relating the ratio of turns to the ratio of...

after learning quantum mechanics, i tried to abandon all intuitions and pictures in classical mechanics however, it seems that the picture in classical mechanics is often valid and useful still is there any good not so naive reference on the quantum-classical correspondence?

I am familiar with the derivation of the probability density function of the sample mean but was looking for an equivalent derivation for the sample median. Does anyone know of a good, clear derivation of this PDF? Thanks, Natski

Urgent-About reference frames! Hi guy's. I thought about this for quite a while but could not convince myself to believe it. I may be wrong somewhere but still any help would be greatly appreciated. The question: Now the Earth rotates at a speed of 7.29*e^-5 rad/sec.,so that any...

Hello Physicsforums, I've been reading here for a while and like this forum a lot. For the following issue I couldn't find a suitable thread so I decided to register and ask my first question: I'm about to apply for grad school, for which I need academic references. I talked to the two...

Okay, in inertial reference frames, two particles with the same charge will always repel each other. Even if they were moving in parallel at high speeds, and thus producing magnetic fields, special relativity would come in and balance the forces from the electric and magnetic fields so that...

Is it possible for a black hole to exist in a reference frame and not exist in another? I did some naive calculations and the result was that what are neutron stars in relation to Earth could be black holes in relation to a proton accelerated near the speed of light at LHC. That is because...

Hi all, I am desperately looking for a reference for a summation formula, which I have obtained with Mathematica. It reads...

Consider an infinitely long straight conductor carrying a current. Let's assume that the free charges in the conductor are positive and are moving at a drift velocity v. Now, consider a particle of charge +q also moving with v in the same direction as the current at a distance r from the...

Does the graviton move at the speed of light in any reference frame? Thanks, Jake

If velocity is subjective to an observers frame of reference, then isn't energy (kinetic) also subjective? How can we define energy as objective if it changes depending on your frame of reference?

Let's consider flat 4D Minkowski spacetime. Is it possible to define (local) coordinate system for any observer (its natural reference frame) so that these coordinates posses interpretation of time and spatial position measured by this observer? It can be done in two dimensional Minkowski...

Does anyone know where I could find a good chart listing the thermal and electrical conductivities of metals? The chart doesn't need to be terribly accurate, I only need to know general values for comparison to other metals on the chart. All I need is one basic value for each metal. If anyone...

Homework Statement I'm using MATLAB show the path of a projectile fired directly up(directly out from the center of the earth) from 41 degrees north latitude. Air resistance, variation of gravity cause by height, and the centrifugal force are for now ignored. What I'm trying to figure out...

Hi, my question is this, say you’re in a lift that is accelerating downwards at 5ms and you were to drop a 200g wallet from say 1.3m off the floor of the lift, assuming gravity is 9.8ms, how long would it take the wallet to hit the floor of the lift? Does the downwards acceleration of the...

Problem: Calculate the velocity and acceleration from an inertial reference frame of a particle whose motion functions (in Cartesian's coordinates) are known from a moving referential. The motion of such a referential is in accelerated translation and rotation with respect to the inertial one...

we generally study the concept of Inertial reference frame in case of translation motion (for non-accelerated frames) what happen if motion is rotational?

Does the concept of Inertial reference frame also applicable for 2nd & 3rd law of motion?

I'm not a physicist and not a mathematician. I just want to understand things, and have read "advanced layman" books. It's often touted that Noether's theorem shows that the uniformity of space (the same everywhere; no preferred origin) implies conservation of momentum. More properly, the...

I tried to check Tex reference when posting - I clicked already existing LaTeX image, clicked "LaTeX code reference" link - and I was aksed to enter user name and password to access protected area :bugeye: Seems like file https://www.physicsforums.com/misc/howtolatex.pdf is protected now for...

Why an accelerated frame of reference is non-inertial?

The other day, I was arguing that a car traveling 70mph rear-ending a car traveling 55mph is the same as a car traveling 15mph rear-ending a stationary car. My argument was that, from the frame of reference of the car that was traveling 55mph, the energy of the other car is k(152), where k =...

Lorentz transformations ("synchronising" reference frames?) Homework Statement A particle moves from (x,y,z,t) = (0 m,0 m,0 m,0 s) to (1 m,1 m,0 m,10 ns). i. What is the speed of the particle in this reference frame? ii. What is the speed of the particle in a reference frame moving...

The fact that the relativity of simultaneity causes events to not happen at the same time, dependent on reference frame, seems to imply a separate universe or world for each and every thing in the universe. Different events at different times due to the relativity of simultaneity would lead to...

This question may be nonsensical, but I have to ask. I'm a noob to relativity so please bear with me. All observers measure the same speed of light, correct? We also know that there is no favored frame of reference. So... what is to stop an object from accelerating to 0.95c, taking a...

Does the principle of invariant light speed still hold in a non Inertial frame of reference? Thank you!

X________________ moving | observer | | ---> v (moving speed train) photon | ^________________| X________________ ^ moving | ^ ^ observer | d1 ^ ^...

Hello, I am trying to understand the relationships of the time scales that obtain within different Inertial Frame of Reference. Not when viewing one frame from another, I am quite happy with the Lorentz factor for that. No it is how the local time scale, that measured by a stationary, local...

STUPID QUESTION ALERT! Is spacetime an absolute reference frame?

To the viewer of this post, What is a good source for the symbols used in a P&ID? I would like to have a textbook or similar which would have all (if possible, or a majority) which I could easily reference to now and in the future when drawing/analysis P&ID's. Kind regards, pavadrin

Hello folks. I am looking to find reference sites which i can use them on my reports and assignments for mechanical engineering and to be helpful. Any help? Cheers

I'm having some trouble with the below vector question. I've got an answer although I'm not sure if it is correct or not. Homework Statement A car travels due east with a speed of 40 kph. Rain drops are falling at a constant speed vertically with respect to Earth. The traces of the rain...

hello forum, i am struggling with the conceptual understanding of this problem: Given two blocks, one on top of the other. There is friction between the two blocks. The upper block is pulled with a force F. Thanks to friction, as long as F is smaller or equal to the static friction...

hello, is there a book that give the proof about how to get the equations of time and the related topics like sun rise time and sun set time and other famous times (sorry i don't know the translation of it in english).

Hello All I have recently recovered from a 4 year hospitalization which pretty much ended my career as a computer scientist. Much of the time I was barley lucid and thus time and medication have taken their toll on my memory. Although I retain much of the theory, I have found my knowledge of...

Hi Guys, I have a problem visualising a free falling object to use as a use as a theoretical reference body. I assume that a geodesic path would be the path that such a body would follow, but surely rotational dynamics would preclude such a situation. If there were theoretically such a body...

ive heard of nano seconds, pico seconds and what not, but I am wondering what the absolute resolution of time is? I am leaning towards infinite

I am trying to find a 2.5V voltage reference, but the only part available in the library I HAVE to use is a 2.5V LDO regulator. I need to have the 2.5V reference supplied from a varying 10 to 16 V source. What are other methods besides a zener or band-gap reference device that I can design a...

Hi, Wondering if anyone can help me with figuring out of if it's possible to make a function on excel with V lookup and IF, if you can pls post an example. Or give an example of using both of these functions in a algorithm to reference to cells on another page in excel within the function...

hi all of u WHAT IS INERTIA? and Earth is a inertial frame of reference or non inertial frame of reference? tell me briefly.

If E=-∇V, does it mean that negative voltage emits positive electric field, and positive v negative ef?

I am interested in naturally occurring electromagnetic waves, is there a reference that lists wavelength, frequency, electric and magnetic fields, etc.?

So if I'm a fast object moving in a sphere, in my frame of reference the sphere begins to contract along the direction I'm moving. As I approach the speed of light, the sphere begins to deform into a disk. If I'm a photon, the sphere is a disk. Rather than requiring requiring 4 coordinates to...