Questions tagged [vibrations]
The vibrations tag has no usage guidance.
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Frequency modes of the rectangular shell
The shapes of three natural modes having the frequencies $w_1$, $w_2$, $w_3$ of the rectangular shell are presented in the figure. The exciting pressure $p(t)$ applied uniformly all over the one side ...
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2answers
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Degrees of freedom of gas molecules
What is the degrees of freedom of a three dimensional polyatomic molecule when only one vibrational mode is excited?
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1answer
150 views
How does a guitar work?
Here are four different possible ways:
The plucked string vibrates longitudinally, vibrating the air around it. This vibrating air then causes the air inside the sound box to vibrate also, which ...
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1answer
45 views
What is quantum molecular movement? [closed]
Q: What is quantum molecular movement? And what are some examples of quantum molecular movement?
I’ve been studying a wide arrange of things but one of the top things I don’t understand is quantum ...
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1answer
63 views
Why do objects have a Natural Frequency? [closed]
Why should an object even have a natural frequency, why not vibrate at any other frequency? This just sounds nonsensical.
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Is this string identity matrix Hermitian?
I found a funny little string identity matrix with left and right real determinants, equivalent left and right transpose, and a null value.
The modes are isomorphic to S0, S1, and S2 circles.
I ...
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1answer
56 views
Are acoustic phonons always the lowest energy vibrational modes in solids?
In solids with unit cells containing more than one atom, the normal modes show acoustic and optical branches. The number of optical branches is proportional to the number of atoms in the unit cell, ...
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0answers
32 views
What is the equation for a convex catenoid, and is it subject to an oscillation on minimum surface?
I want to re-think the shape of a vibrating string to find a source for frequencies that are not emitted by the fundamental mode but do not require points that are fixed and moving at the same time, ...
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1answer
17 views
Change in vibrionic energy in at atom at a higher excited electron state
I was studying the coupling of Vibrational and Electronic energies and was left confused at one aspect of the subject.
Consider the image showing a transition from one electronic state to a higher ...
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1answer
36 views
Coupled pendulums at half height
Suppose we have the system described below (poor quality but it'll do the trick). We have two pendulums of mass $m$ coupled by a string of constant $k$ placed at a height $a$ from the top (as shown). ...
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1answer
39 views
Natural and Driving Frequency of a Spring-Mass System
Does $$f = \frac{1}{2\pi}\sqrt{\frac{k}{m}}$$ measure the natural frequency or driving frequency of a spring-mass system? I can't find any resources which confirm this!
I believe it measures the ...
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2answers
71 views
At what frequency does a string vibrate?
When a string with fixed ends vibrates (e.g. plucking a guitar string) Fourier Theorem says that the vibration can be expressed as a sum of its normal modes, which are sinusoidal vibrations with ...
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0answers
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Acoustic waves in multilayer materials
In a thin homogeneous material the acoustic wave obey the standing wave condition with a period of T = 2 * sample thickness / velocity of sound. Let us assume we have a very thin three-layer structure ...
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1answer
42 views
Relation between shapes and vibrations
I have observed the following shape on surface of water when the bottle was standing on a cooling water machine. I was amazed by the formation because I had not seen this before. I'm not completely ...
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Wave Equation Using Symmetry Argument
In Howard Georgi's The Physics of Waves, one chapter discusses space-invariant symmetry on the classic beaded string. From the symmetry matrix, we can then derive complex normal modes and the ...
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0answers
24 views
Derivation of an eletrical signal propagation
I am currently undergoing a physics course about the physics of waves and vibrations ( actually following "The physics of vibrations and waves" from H.J.Pain) and I came across the coupled oscillators ...
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1answer
25 views
Tuning a tuned mass damper
In order for a tuned mass damper to work effectively, its frequency and damping ratio have to be tuned according to the mass ratio of the damper and the whole system itself, such as by using the Den ...
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2answers
36 views
Do we need a small displacement to create a oscillatory motion on the spring?
Do we need a small displacement to create a oscillatory motion on the spring with a mass attached to it? Whats the limit of the displacement that we can give initally to create a oscillatory motion? ...
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0answers
17 views
Different ressonant frequencies for velocity and displacement
For a damped oscilator, by working ou the math one can easily see that the ressonant frequency for the displacement is slightly lower than the one for velocity. But why? How we see this intuitively?
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1answer
52 views
Event Horizons Vibrations
Can the event horizon of a black hole vibrate? If so, are there mechanisms that dampen the vibration?
Consider a spherical, non-rotating, non-charged black hole located far away from other sources ...
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2answers
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What is the difference between solutions to 2nd order homogeneous ODE?
I’m studying Vibrations, and we have two forms to the 2nd order homogeneous ODE:
$$mx ̈+kx ̇=0$$
$$x(t)=C_1 e^{iw_n t}+C_2 e^{-iw_n t}$$
and
$$x(t)=A\cos(w_n t)+B\sin(w_n t)$$
Even though I can use ...
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2answers
50 views
Degrees of freedom for diatomic molecules [duplicate]
I have a doubt in understanding about the degrees of freedom (dof) ......as I have learned dof is nothing but the necessary parameters to specify the location and configuration of a system.....if that'...
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1answer
85 views
How is temperature related to quantum vibrational states of molecules?
When a molecule of greenhouse gas absorbs a photon of long wave infrared radiation it is boosted to the next allowed vibrational state. The vibrational state, as I understand it, involves deformations ...
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1answer
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Why does acoustic imepdance increase when mass density and bulk modulus increaes?
If we take some material and (somehow) increase its mass density or bulk modulus then its acoustic impedance will increase as $z = \sqrt{\rho \kappa}$. That is, it What is the physical reasoning ...
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1answer
279 views
Using the Debye model, show that the contribution of the zero point energy to the lattice vibrational energy is given by $𝑈=(9/8)𝑁𝑘_B𝜃_𝐷$
Using the Debye model, show that the contribution of the zero point energy to the lattice vibrational energy is given by $𝑈={9\over8}𝑁𝑘_B𝜃_𝐷$.
I know that The zero point energy is $E={1\over2}\...
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1answer
52 views
Why consider only real part when summing several simple harmonic motions?
I have been studying vibrations and I stumbled upon the overlapping of simple harmonic motions. Consider the case where the number of oscillators $n$ is $n \gg 1$, all of them have the same angular ...
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1answer
86 views
How to determine if a calculated Raman mode in a crystal is active or not?
I have used an ab initio electronic structure code to calculate the harmonic Raman spectrum of a (molecular) crystal. However, no use of symmetry has been made, and it might well be that some of the ...
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2answers
59 views
Boundary condition: displacement
I have a controversial case. I have a rod, which is fixed from one end (constraint). From another end, I apply a compressive force, by pressing the rod down. So in a way I have a constraint, but at ...
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1answer
119 views
How does one mathematically derive the damping coefficient of a theoretical viscous dashpot?
I am very well aware of how to get the damping coefficient experimentally by observing a system in action.
Given the dimensions and fluid properties of a theoretical viscous fluid dashpot, how does ...
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1answer
154 views
2 Extra Degree of Freedom in Linear Triatomic Molecules?
Ok, there is a bit problem in understanding Degree of Freedom of Linear Molecules specially of Triatomic Linear Molecules.
See, the DOF in general is given as $f=3N-k$.
Here,
N=Number of atoms in a ...
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2answers
43 views
For a molecule, does the term 'thermal vibration' mean the same thing as 'molecular vibration'?
When speaking of a molecule, do both terms ('thermal vibration' and 'molecular vibration') describe the same thing, being the one and only periodic motion of the atoms within the molecule?
Or, are ...
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1answer
29 views
Tools for measuring vibration/sound of shaking
I would like to know how I can measure the vibration coming from my hand shaking something. My experiment is like this. I put a ball made of strong glass into a closed empty box made of strong glass ...
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2answers
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Actual Degree of Freedom of Diatomic Molecule
Ok, I have 2 very different values for degree of freedom(DOF) of diatomic molecules arising due to the difference in the vibrational DOF of the diatomic molecules.
According to this DOF wiki page:-
...
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0answers
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Justification for using wave equation for describing a phenomena
I have recently started learning about waves. We didn't really formally describe what a wave is, but instead started by looking at a concrete example namely harmonic sinusoidal waves in 1d.
We then ...
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1answer
135 views
What is the difference between sound and vibration?
As far as I know, the only difference between sound and vibration is that sound propagates but vibration does not. In most cases, they are the same.
Please help clarify these concepts.
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3answers
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Why this incident happens? [closed]
If there's a rope which two sides are attached to the wall and a rigid body is hanged down from the rope (that body has light mass )in a such situation if a force is applied on the rope at any point ...
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1answer
35 views
Is the fundamental mode the only mode produced in free vibration?
Let’s say I strike a 2D circular plate with some impulse. Is the fundamental mode the mode that’s always being produced, or is it possible to sustain only higher modes such as a (1,1) mode etc.
Let’s ...
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1answer
60 views
Why does change in tension of a vibrating string result in infinite acceleration of an atom at the transition point?
Consider an infinite uniform vibrating string centred at $x=0$ and extends from $+\infty$ to $-\infty$ whose tension is to be changed at x=0.Instead of just changing the tension directly we introduce ...
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2answers
157 views
Does a vibrating string produce changes in tension in the string?
A taut string anchored at both ends increases in tension as the string is displaced to a side. When released the string will vibrate at whatever frequency to which the system is tuned.
If this were ...
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2answers
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Vibration of strings [duplicate]
What happens if we clamp a string at both it's ends and pluck it at different distances from one of the ends? Will the frequency of oscillation be the same or will it differ based on the place from ...
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0answers
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Seismology - PPV / VDV from geophone waveform data
I'm using an inexpensive seismometer to try and measure the effects of local HGV traffic on buildings. The device is connected to a Raspberry PI that has a Cirrus Logic Audio Card. The signal is fed ...
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0answers
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Coupled mechanical systems
Consider a coupled mechanical system, as an example take two vibrating strings. These will be coupled by a rigid massless link.
Say we are calculating a transfer function $H$ defined as
$$ H = \...
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0answers
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Eigen-Energy of Vibration on a Loop
I recently started this recreational project to find the energy of the modes on a loop. To obtain the eigen-energies $E_n$, I decided to solve the 1D wave equation on a loop of circumference $2\pi l$ ...
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1answer
43 views
How can i slow my molecular vibration so objects can pass through me without injury [closed]
The goverment has already developed it combined with a light refraction suit
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1answer
134 views
Does a hollow sphere vibrate longer than a solid sphere?
Assume the following are constant:
Surface area of both spheres
The spheres are both made of titanium (Ti).
Mechanism that strikes a given sphere delivers the same energy per strike.
Spheres are ...
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5answers
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Does plucking a guitar string create a standing wave?
About two weeks ago there was a mock test in Korea, and a physics question asked if a plucked guitar (it was actually a gayageum, a traditional instrument, but I'll just call it a guitar for ...
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1answer
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Calculating the decay rates for modes of an ideal circular membrane (ie. drum head) using wave equations?
I am attempting to solve for the theoretical decay rates of the various (m,n) modes of an ideal circular membrane, if that membrane is excited momentarily by an impulse or deformation.
I would ...
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raman tensor of graphène and its polarisability
I want ask about the raman tensor of graphene
all that I know, the raman spectrum of graphene has 2 main peak G and 2D.
but what about its tensor raman.
I know that the metals materials don't have ...
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1answer
115 views
Fourier Series Analysis [duplicate]
Can anybody explain this paragraph from the chapter " Fourier series and transform " of the book by M l Boas?
"If you strike a piano key you do not get a sound wave of just one frequency . ...
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1answer
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What is the difference between the dipole in IR and Raman vibrations?
In order for a vibration to be IR active, there must be a change in the dipole moment ($\mu$) of the molecule, which is given by:
$\mu$ = $\sum$ q * r
Where q is the charge magnitude and r is the ...
