Tag Info

Hot answers tagged

52

A sonic boom is produced when a macroscopic object (say, roughly: larger than the average spacing between air molecules, $\approx 3\,\mathrm{nm}$) moves so fast that the air has no time to “get out of its way” in the usual way (linearly responding to a pressure buildup, which creates a normal sound wave that disperses rather quickly, more or less ...


32

I know that when an object exceeds the speed of sound[340 m/s] a asonic boom is produced .Light which travels at 300000000m/s [much more than the speed of sound] doesn't produce a sonic boom right? Why? The answer is already in your own question: just because light is not an object. Sound "is a vibration that propagates as a typically audible ...


17

There are many differences between light and sound waves noted in other answers, such as the impossibility of any object with nonzero rest mass reaching lightspeed. However, there is one likeness that I don't think has been noticed yet and that is the following: a sound wave travelling at the speed of sound does not make a sonic boom! This is because the ...


13

Have a look at the article by Phil Gibbs on the relativistic rocket. This describes the motion of a rocket that is accelerating with a constant acceleration. In this context constant acceleration means the crew of the rocket feel a constant acceleration. Technically the rocket has a constant four-acceleration. Anyhow, the velocity of the rocket as observed ...


6

Is there some other formula ... which ... does not allow the speed ... to surpass the speed of light? That would be the equations of special relativity mentioned by sahin in a comment. Image from Loodog? Another factor you have to take into account with classical mechanics is to work out how a constant force can be applied to your object over 11 ...


5

The light from the observation point that hit the mirror and returned would be two years old by the time it returned to the observation point, but there is a very big problem with this set up. The mirror would have to be huge and curved to reflect enough light from the observation back again so that it could be seen. (Imagine tyring to brush your hair in a ...


3

It's a mixture of $c_\infty = c_0 = c$ and "the question doesn't make sense". So, first, how it does not make sense: What's the "speed" of a quantum object? It has, in general, no well-defined position, so $v = \frac{\mathrm{d}x}{\mathrm{d}t}$ is rather ill-defined. Instead, we should probably look at the mass of the photon, since all massless objects ...


2

You can store light up to one minute so far. Basically you make a crystal transparent (low OD) at a predefined desired wavelength. When the light pulse goes in, you turn the crystal opaque (high OD). You retrieve the pulse by making it transparent again at the right time. The material is some Pr-doped crystal. For this purpose, it is hard to find a material ...


2

There is no contradiction. From your quote: The proper length of an object is the length of the object in the frame in which the object is at rest. and The proper time between two events - such as the event of light being emitted on the vehicle and the event of light being received on the vehicle - is the time between the two events in a frame ...


2

The light emitted before the shut off of the sun will definitely reach the earth and it will take 8 minutes. Which means, you will not know for 8 minutes that the sun had stopped producing light.


2

Feynman: The correct picture of an atom, which is given by the theory of wave mechanics, says that,so far as problems involving light are concerned, the electrons behave as though they were held by springs. So we shall suppose that the electrons have a linear restoring force which, together with their mass $m$, makes them behave like little oscillators, ...


2

Jon Custer hinted at something, which I think is best explained via an analogy. Imagine you can walk along a pavement at 4mph. When the pavement is empty, it takes you an hour to travel four miles. But when the pavement is crowded, you're dodging around people and bumping into them. You're still walking at 4mph, but it takes you an hour and a half to travel ...


2

Have a read through my answer to What is so special about speed of light in vacuum?. From popular science articles and TV programmes it's easy to get the impression that the speed of light is, well, just some speed. However it's intimately related to the geometry of the universe, and as such is one of the most fundamental properties of our universe. In ...


2

A stellar mass black hole usually forms during a core collapse supernova of a very massive star. Our understanding of star formation is that most stars will have some angular momentum, and some of this angular momentum will be passed on to the black hole which is produced when the core collapses. This means that, as you mention, most black holes will be ...


2

The local speed of light is always $c$. Local in this sense could mean that for each observer there exists a neigborhood of that observer such that, if we call $v_c$ the "observed speed of light", $|v_c - c| < a$ where $a$ is arbitrarily small. However $v_c$ is a slightly nebulous concept as beyond the inertial frames in special relativity, there ...


1

There is no limit to the velocity that a person may travel. However, there is a limit to the acceleration that a person can handle. This is complicated as that maximum acceleration depends on how long the person is at that acceleration, how fast they got there, their muscular structure etc. The shorter time you have an acceleration the greater that ...


1

Look at sparknotes.com/physics/specialrelativity/dynamics/…, you can see $dE/dx=F$ - if your force is constant, it is the energy that increases constantly. $E=\gamma(v)m_0c^2$, you can deduce the $v$. Beacause of laziness I used mathomatic, and it gives me something like this: $v=c\sqrt{1-\frac{m_0 c^2}{(F\cdot x + m_0 c^2)^2}}$ If you check it for x=0 and ...


1

I don't really see a difference between the microwave measurement and the definitions of the SI units. We have Unit of time: second: The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. Unit of length: meter: The ...


1

The experiments of John Bush on pilot-wave hydrodynamics have evidently proven that macro-scale replication of quantum effects is entirely possible, the Copenhagen interpretation may be in trouble, and the answer to your question may end up being "yes," after all, to the surprise of most all of us. That being said, until more experiments are done, I doubt ...


1

It is a standard exercise in most quantum field theory books that the 2-point function does not vanish outside the light-cone of a particle. Less technically; the probability that some particle $r$ away from a source feels the effect of the source quicker than light to travel would $r$ is non-zero. That is a good definition of superluminal motion. See for ...


1

Is the speed of light affected by all mediums it travels in? Yes. Including space, but don't get distracted by virtual particles. The speed of light varies with gravitational potential. Search the Einstein digital papers on "speed of light" or "velocity of light" for examples like this: Also see Shapiro's 4th test of General Relativity along with The ...



Only top voted, non community-wiki answers of a minimum length are eligible