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0answers
17 views

Waves velocity for a standing wave of a string

I have done a laboratory experience to determine the speed of propagation of a wave in a vibrating magnetic string. To calculate the frequency (f) of oscillation I used an oscilloscope that calculated ...
1
vote
1answer
57 views

How fast will air travel to fill a vacuum?

Suppose I have a sealed glass cylindrical vessel of radius r and length l that is evacuated. I smash one end. How long will it take for air to (a) reach the end of the cylinder (b) fill the vacuum ...
1
vote
2answers
93 views

Problem in finding the velocity of a wave

In my textbook, the equation for a wave is described as : $y = A \sin{\frac{2\pi}{\lambda}(vt-x)}$ Now in this equation $x$ is variable as well as $y$. So when we will differentiate the equation by ...
0
votes
1answer
51 views

If 2 spaceships approaches each other at 0.99c, how much blue shift would they see? [closed]

Imagine these 2 spaceships moving at 0.99c toward each other and speed isn't additive how much blue shift would they see? I know how to calculate when the scenario is spaceship vs Earth but how about ...
0
votes
1answer
56 views

What is the interpretation of speed of a travelling wave, based on $\frac {\partial x}{\partial t}$ formula

Motion satisfies the wave equation if the following holds true $$\nu^2 * \frac {\partial ^2 \psi} {\partial x^2} = \frac {\partial ^2\psi} {\partial t^2}$$ where $\psi$ is the vertical displacement ...
1
vote
0answers
25 views

When is the group velocity of a wave packet the velocity of energy flow?

In particular, I'm asking this for anisotropic media
0
votes
2answers
815 views

The relation between speed and wavelength

I was taught categorically that the velocity of a wave depends only on the medium in which it travels. Now I just stumbled upon a sentence + formula that declares that "the velocity of sinus-waves ...
1
vote
1answer
102 views

Intuition behind group velocity

Why is the group velocity of the wave given as $\frac {\partial w }{\partial k}$? I understand what the group velocity means but its always given as a definition and I would like to have some ...
1
vote
2answers
191 views

How come group and phase velocity can be different in a non-dispersive media?

I'm a (ex-)physicist working in the applied-physics world and was digging into group vs phase velocities. There is one thing that confuses me : when would that be the case where group and phase ...
2
votes
2answers
201 views

Sound tavels faster where?

We know that sound travels faster in a water than air. Also water is denser than air. So sound travels faster in a denser medium. But we know that sound travels faster in a warmer air and warmer air ...
6
votes
2answers
214 views

Understanding group velocity

Group velocity as a concept in Classical Waves confuse me. It's very easy to point out visually, like in this really helpful graphic here. Okay, it's the speed of the moving bulge, which, notably ...
2
votes
1answer
7k views

Are these definitions for transverse wave velocity on a string consistent?

I've found two definitions for the velocity of a transverse wave on a stretched string: $$ \begin{align} v & = \frac{\omega}{k} \tag{1} \\[10px] v & = \sqrt{\frac{T}{u}} \tag{2} \end{align} $$ ...
1
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0answers
80 views

A wave on a vertical rope [duplicate]

I'm taking a physic class and there is a problem that I'm not sure how to answer. It goes as follow: a heavy rope is tied to the ceiling. Someone jerk the rope. How will the speed, the wavelength and ...
36
votes
3answers
4k views

Is it possible to estimate the speed of a passing vehicle using a musical ear and the doppler effect?

I've found a number of questions that concern the Doppler effect, but none that seem to address my question. I have a background in music. People with a musical ear can generally tell the ratio ...
3
votes
3answers
521 views

Velocity of a Mechanical Wave on a String

I recently read a derivation for an equation which governs how quickly a wave is transmitted along a string, $v = \sqrt{\frac{T}{\mu}} $, where T is the tension in the string, and $\mu$ is the mass ...
0
votes
1answer
102 views

What is the speed of sound in a rigid body?

A rigid body has particles which never move. So will no sound travel through it ?
2
votes
2answers
300 views

Does the velocity of water waves increase with the kinetic energy of an object dropped to create them?

I'm doing a experiment that revolves around dropping an object into a container with water. When I increase the mass of the object, will the velocity of water waves increase when the object is ...
1
vote
2answers
109 views

$\omega(k)$ and $k(\omega)$ about waves

Wave propagation is characterized by the wavenumber $k$ and the angular frequency $\omega$. Sometimes (like in this answer) the relation $\omega (k)$ is preferred; sometimes instead $k ( \omega)$ is ...
1
vote
1answer
443 views

Group velocity with gaussian pulse

A gaussian pulse wave propagating in a non-dispersive medium with velocity $v$ can be expressed as $$h(z,t) = e^{-a(t - z / v)^2}$$ as suggested in this answer. In the case of a dispersive medium ...
3
votes
0answers
137 views

Envelope of wavepacket and group velocity

In this answer a possible derivation of the group velocity is provided. It is, anyway, based on the assumption that there will always be a point where all the cosines will sum with the same phase: ...
4
votes
1answer
173 views

Christmas Question

Is it still christmas day? I just lit the christmas pudding. For those unfamiliar with this tradition, one pours alcohol of sufficient concentration over the pudding and makes a bit of fuss around ...
0
votes
1answer
118 views

Group Velocity of guassian packet equals time derivative of mean position?

If I look at a gaussian wave package, and then interpret (in the usual Quantum-Mechanics Way) its square value as the propability density, then I can calculate a mean value for the position: $$ x_{...
1
vote
0answers
183 views

Meaning of a Dirac delta speed in 1d shallow-water equations

A 1d thin layer of a fluid of constant density in hydrostatic balance can be modeled by shallow-water equations: $$\begin{align*}\partial_tu+\partial_x\left(v+\frac{u^2}{2}\right)&=0,\\ \...
0
votes
1answer
317 views

Trasversal wave on a rod velocity

What is the velocity of a trasversal wave on a metal rod? Does it depend on the shear modulus $G$ $$v_{t}=\sqrt{\frac{G}{\rho}}$$ Or on the tension $T$ of the rod? $$v_{t}=\sqrt{\frac{T}{\rho}}$...
5
votes
3answers
527 views

Transverse Wave [closed]

Tranverse Wave is travelling in a string.
0
votes
1answer
77 views

Velocity of propagation of an EM field in vacuum

I am asked to find the speed of propagation $\vec{v}$ of an electromagnetic field, in a region of empty space. The magnetic field is described by $\vec{B} = B_0e^{ax}\sin{(ky-\omega t)} \hat{z}$. I ...
-1
votes
1answer
650 views

What is meant by 'Phase velocity is $c^2/v$' [closed]

Is phase velocity $c^2/v$ or $v/2$? Is there only one phase velocity as indicated by the above formula? If yes then why is wavepacket said to be superposition of 'waves' whose velocity is termed as ...
1
vote
0answers
701 views

What is the relationship between the velocity of an object and its Sound Intensity Level in an inelastic collision?

Assuming the mass, acceleration, and height of the dropped object are constant and the area of the measured sound wave is constant, would the relation be linear, exponential, logarithmic, square root ...
1
vote
0answers
82 views

Resolving multipath interference when modelling radio wave propagation

I am creating a raytracer to model the propagation of radio waves from a simple router. I am assuming that the rays have a frequency of 2.4GHz and a velocity of the speed of light. The router has an ...
6
votes
1answer
15k views

Longitudinal Waves - how velocity varies with density

The formula for finding the velocity of a longitudinal wave, such as a sound wave, is: $$v = \sqrt{\frac{E}{\rho}}$$ Where $v$ represents the velocity, $E$ represents the elasticity of the medium, and ...
2
votes
1answer
1k views

If wave speed is dependent on medium only, then how to reconcile $v\propto f$?

I have read and learnt in many places that velocity of a wave depends only on the medium through which it travels. It is clear from this that the velocity of a wave doesn't depend on the frequency of ...
0
votes
3answers
171 views

Does there exist a hyperbolic relationship between frequency $\omega$ and wavenumber $k$?

As the title states, is it possible to derive a hyperbolic relationship in the form of $\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1$ between frequency $\omega$ and wavenumber $k$ I have tried to start this ...
0
votes
3answers
12k views

Why frequency is inversely proportional to time-period?

Why frequency is inversely proportional to time-period? While studying about Fourier transform that shows frequency representation. A doubt that came to me was a set of signal with same wavelength but ...
1
vote
0answers
585 views

What is the physical explanation for the phase relationship between acoustic pressure and particle velocity in plane and spherical waves?

I've been looking around for a decent physical explanation of the differences in the phase relationships between acoustic pressure and particle velocity in different types of waves. Mathematical ...
0
votes
0answers
820 views

Wave Packets, Group velocity, and Phase velocity [duplicate]

Mathematically, you find that the wave function of a particle $\Psi (x,t)$ moves with the same velocity as the velocity of the particle ($v_{particle} = v_{group}$). Is there a reason why the ...
1
vote
1answer
766 views

Displacement of an object due to opposite and equal forces acting at different times?

This question is about mechanical waves in solids, the speed at which forces propagate through solids, and the displacement that might occur due to unequal starting times of equally sized forces. ...
23
votes
1answer
3k views

What determines the speed of waves in water?

While I was walking my dog this morning, I passed over a canal filled with boats, barges, and kayaks all of different masses and moving at different speeds. I noticed that all of these vessels left ...
2
votes
2answers
3k views

Deriving the group velocity of a wave produced by some basic cosine waves with unequal amplitudes

Consider some basic cosine waves of the form ${E_i} = {E_0}\cos ({\omega _i}t - {k_i}z)$ with different amplitudes, frequencies and phases. We know a combination of such waves could result in a wave ...
2
votes
1answer
560 views

Isn't the front edge of a wave, kind of “information” which travels faster than light?

Considering the definition of phase and group velocities, We know group velocity can't exceed C but phase velocity can be infinitely high. Assume a monochromatic electromagnetic wave traveling with a ...
2
votes
2answers
6k views

What does the velocity of a wave mean?

I know that the velocity of a wave is given by $v=\lambda f$ but what does this velocity represent in the physical sense. For instance, if I am told a car moves at a velocity of 5 $m/s$ I know that ...
4
votes
2answers
8k views

Group Velocity and Phase Velocity of Matter Wave?

In quantum mechanics, what is the difference between group velocity and phase velocity of matter wave? How can it also be that phase velocity of matter wave always exceeds the speed of light?
2
votes
3answers
17k views

How do you find the velocity function of a mechanical wave?

With the form $y(x,t)=A\sin(kx-\omega t+\phi_0)$, there are two variables, How do I find the velocity? I don't know I can apply derivative with two variables.