Speed Definition and 999 Threads

Why do we know the velocity of all photons are the same as the velocity of light?Can we deduce this or we must have experiment test?What is the experiment test?

Hi. This is an idea which I just happened to think of, and I was curious if it would be at all feasible. Here's a quick sketch I drew: The two curved mirrors should have a laser attached on one end and a video camera attached on the other. The laser would be tilted very slightly above...

Does anyone know what the minimum speed of a gyro to make it so a force at 0deg will yield a movement at 90deg... or even better, what the angle is wrt speed... see http://www.copters.com/aero/gyro.html for pictures. -thx, rich

Hello Forum, The speed of efflux ##v_{efflux}## of a liquid, say water, from an orifice in the lower part of a container depends on the vertical distance between the free surface of the fluid and the lower position of the orifice in the container itself. The faster the speed ##v_{efflux}## the...

As in Bernard Schutz's A first course in general relativity, page 220, we suppose a gravitational wave travels in the z-direction with pure "+" polarization, so that the metric in the TT coordinate system is given by$$ds^2=-dt^2+[1+h_{+}(z-t)]dx^2+[1-h_{+}(t-z)]dy^2+dz^2 .$$ Suppose that two...

I have a Intel(R) Xeon(R) E-2274G CPU @ 4.00GHz 4.01 GHz machine which has a published max speed of 5.0 GHz. However, when I run it under load on all 4 cores, it only gets up to about 4.5 GHz: Could someone explain to me why it's not ramping up to the full 5.0 GHz or what I could do to...

Are the following statements true? --------------------------------------------------------------- If a speaker and a listener are stationary with respect to the air, a listener will measure the speed of sound at about 343 m/s. Since the speed of a sound wave in air is dependent only on the...

First calculated non conservative work from friction using Ff=umg. Non conservative work was -8.82. Initial kinetic energy, 1/2mv^2, was 136.89. Change in potential energy, 1/2k(x)^2, was 8.1216. Ekf-Eki+Change Ep=Work NC Ekf=W NC+Eki-change Ep =-8.82+136.89-8.1216=119.9484 Ekf=1/2mv^2...

its has been said that light slows down in glass, but some talk about phase velocity and group velocity... then there is the velocity of the photons, which some say is always c. What are those speeds [Vgroup, Vphase, Vphoton, Vlight] in glass, and what do they mean?

Hi everyone Could someone explain what happens in the body when metabolism speeds up? For example, does it produce more stomach acid? Or does it produce more concentrated stomach acid? Thanks

Starting from the microscopic form of Maxwell's equations and following standard mathematical procedure outlined in Inhomogeneous electromagnetic wave equation - Wikipedia we can have as end result the following equations: $$(\nabla^2-\frac{1}{c^2}\frac{\partial^2}{\partial...

So to cut to the chase, I missed my class' lesson on momentum - have tried to catch up, quite successfully but am baffled about this question. I know the conservation of momentum etc. but after trying for ages it's just not happening this question so any help would be much appreciated, Oscar.

Hi Pf I read that in the light propagator there are loops of electrons. What would be the consequences if we could switch them off (or neglect them)? would it modify the speed of the photons?

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-14/circuits-and-the-speed-of-light/ Sorry, my other post must have been too brief. In another thread shut down by Dale, this very site (allaboutcircuits) was used by him to reference wave guides. This particular page is 100%...

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-14/circuits-and-the-speed-of-light/Hmmmmm. :))

The topic here is about the speed that the "electrical" signal (impulse) travels at in a copper wire. The speed is well known to be just under c. Often when this topic is spoken about, the term "EM field" is used and I don't understand why. We have electrons with a power supply that supplies...

Hi, I'm thinking about buying a fast laptop with 4 cores but I've never been quite clear just how fast they run. Here's the description of the CPU from HP's website: Does this mean that if I set up parallel processing on all cores, each core "can" run at (or near) 4.6 GHz or the combined sum...

Theoretical experiment for measuring one way speed of light From 1905 to this day we have not experimentally measured the one way speed of light between a source to the detector only the roundtrip from the source to the detector and back again. We just assume that the speed of light is the...

Considering the device above, which uses electric and magnetic fields placed properly to avoid charged moving particles with velocities different from the ratio ##\frac{E}{B}## to exit, getting deflected upwards or downwards. All that is easily demonstrable by equalling the forces acting on the...

I'm trying to turn my milling machine into a CNC so I bought this motor driver on ebay. https://www.ebay.com/itm/DC-40A-DC-Motor-Speed-Control-Reversible-PWM-Controller-12V-24V-36V-48V-2000W/173177079359?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 The only problem is I can't...

I'm probably am wrong in this but i guess you guys could light me in this one

Note, it possible to determine if the speed of light varies depending on direction, with the use of a single clock. Simply send a beam and reflect it back, but on the return trip introduce a medium to slow the beam. Three cases, T1, T2, T3 are total travel times. T1: assume light is the...

First, I am way out of my field of understanding here so please keep it simple. I watched some videos on E=MC2 which led to how light reacts differently than matter at high speeds causing time to slow down when moving fast. My question is, if I was to shine a flashlight perpendicular (90...

Is it really possible for light to travel at different speed in opposite directions? This video seems to say that this is assumed as a fact (with of course Einstein being the one to make the assumption), and that since it is impossible to measure the speed of light in one direction, we really...

Visualize the following scenario. A star such as the sun, and a planet such as Earth are located in a solar system. A photon travels from sun (x0) to Earth (x1), and a satellite is in the midway observing the photon. This is relates to Einstein's special relativity. I ask this since it take...

Now this is how I've tried to solve this $$ v_e = u0 \cdot ln \frac {M} {M- μ \cdot t} $$ After putting in the values I get this; $$ v_e = 200 * ln 0,36 $$ $$ v_e = 73,54 \frac m s $$ Now I'd say that this is the correct way to do it, but this part is confusing me "What is the speed of the...

Does this video even make sense? And if so, is it right or wrong?

I started by finding the main events: Sending the first message Receipt the first message Sending the second message Receipt the second message Now, what we know is the time by ##S'## (comoving frame with the spaceship) ##T_1'## and ##T_2'## remaining to arrive to the Earth measured at...

I'm really not sure how to start this one!

I have a question regarding Kugelblitz black holes. I know that they are purely theoretical, and I am perfectly fine with the matter-energy equivalence so I have no problem in assuming that concentrating a sufficient amount of energy in a certain radius might generate an event horizon. However...

Hello, just some general questions I have been thinking about 1. So as you approach the speed of light time slows down, but why not at everyday speeds like walking around? I know people are going to say time slowing down only matters at extremely high speeds. However, shouldn't time dilation...

I know the solution is based on velocity and the sliding friction coefficient, and I believe I should put the condition Fcf smaller than Ff, but I just don't understand how to include μ in the solution, to find the angle. Even if you don't solve the problem, I just need to understand the...

In the USA, ordinary citizens pay different tax rates for "long term capital gains" versus "short term capital gains". What rates do organizations that do high speed stock trading with computers pay? Are all their profits short term capital gains? Or do they establish themselves as...

Hi, I am working on a project that would insert a generator/expander system to a pressurized stream of gas in order to generate electricity. I would like to control the rotational speed of the generator in order to adjust the gas stream flow rate. Would it be possible to control the...

Hi PF It's a multiple choice exercise, and the answer is 10 m/s. I've been wondering why, but no way. Regards

If many quasars are at redshift 10, and another group is at redshift 6, what is the speed of the second group relative to the first? The redshift 10 group can be considered "at rest", so the redshift 6 group is heading in our direction at what rate? For this scenario, let us assume all the...

In every single question asking about the maximum height you get from jumping in 2 different planets they consider that the speed you leave the ground is constant. Why is that? Speed would be constant if impulse were constant. Impulse would be constant if both force and time were constants...

If you want to detect a particle in the 2 slit experiment on a detector. And we state that the electron is traveling as a wave so there is a wave front...that must mean that the wave front hits the detector at the same time in more than one place where there is constructive interference. But...

I wanted to ask this question for very long . lets say we have rocket in mass of 1kg in space that moving in speed of 100 m/s if we want the rocket to speed up, we need to spent some energy that equal to mv^2/2. in our case it 1*200^2/2 it 2000 Minos the energy we already have which is...

Neglecting the air resistance, is it more difficult for a biker with a proper gearing in his bike, to increase his speed by 5 kph if his current speed is 20 kph rather then if his speed is 10 kph? It seems that the answer is yes according to the energy formula but I've asked several bikers and...

Being honest, I couldn't do any works for this problem... (even couldn't start...) Does anyone can help me for solving this...? Thank you!

I've read that speed of light for a Rindler observer is not constant. I wasn't sure why and I tried to do this as an exercise for myself, I think I came with the correct answer, but I'm not sure, is the following argument correct? Let's describe the (flat) space-time using Rindler coordinates...

If sound (or any wave) was transmitted in a medium whose density was vanishingly low , would that wave propagate in the same way as em radiation in a vacuum? And vice versa does em radiation propagate in the same way as ,say sound so long as it is in a dense enough medium? In other words...

If the answer is yes then it seems that Einstein's second postulate was not so revolutionary.

This probably has been asked before but i had a thought about the speed of light and time dilation. First off all i know the speed of light is constant and that it is the max speed anything can be but hear me out. So let's say a jet are traveling from point a to b in space with let's say 0,8c...

I attended to many attemps and I not able to find out no dependencies in this layout. Does someone can show me how to solve this problem step by step? What we must take into considarion in solving such tasks?. How to start?. I got stuck. This task is from Polish Physics Olympics.

This is a long post with limited amount of physics in it (but it is a physics question, so hopefully it is allowed). I am a scientist but trained as an ecologist (PhD) and despite my long interest in physics, my knowledge of it remains rather rudimentary. Apologies for that, in advance. I am...

I have seen the solution and understand it. The solution defines θ to be the angle between the falling rod and the table. It then equates initial PE to the final (PE+KE) where the final PE=0 and the final KE to be (1/2) Iω2+ (1/2) ma2ω2 to finally obtain ω = √(3g/2a) But i would like to know...

Need some help on how to solve the integration formula for Maxwell speed distribution, here is the procedure on how to solve for the kinetic energy: Not familiar with the error function yet, but the result for the kinetic energy integration is...

Dear all, I have a very simple question. The rolling resistance (rr) of, say, a car, is defined as being proportional to the normal force/weight of an object. That seems reasonable: ##F_{rr} = C_{rr} \times F_N## The coefficient C_{rr} is a constant, depending on the materials. But now a...