Questions tagged [vibrations]

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2answers
66 views

The Strings have a finite size they can vibrate?

as I searched about the Strings theory I found out this explanation: Since the strings have a finite size they can vibrate. All the known particles of nature are just different modes of vibration of ...
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2answers
74 views

What makes quartz oscillators vibrate?

I understand that the principle behind it is piezoelectricity and electrostriction (inverse piezoelectricity), but how does one make the crystal vibrate? The only thing I can think of is using an ...
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5answers
304 views

What is the reason behind resonance?

At the technical highschool that I attend, the instructor said that the cause of resonance is that energies increase differently. Kinetic energy increases quadratically and potential linearly, so the ...
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1answer
44 views

Heat capacity due to Phonon Vibrations

Why does the speed of sound come, in the expression of Heat capacity, from phonon vibrations?
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69 views

Faraday waves and Chladni plates

I am a High school student who's writing a research paper about Faraday waves and Chladni plates. I've been doing a lot of research on Faraday waves specifically, as there aren't many sources that can ...
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1answer
128 views

Optical and acoustic branch

Does a diatomic crystal posses both optical and acoustic branch simultaneously; Or, whether the vibration is either optical or acoustic?
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1answer
61 views

Why standing wave conditions don't include a phase difference of π

So in order to set up a standing wave on string I can set a travelling wave on it first then let this travelling wave get reflected from a fixed end and this reflected wave interferes with the ...
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1answer
61 views

What will happen to these colliding strings?

What happens when these two strings collide? Do they cancel each other out, pass through each other or interact in some way? Thanks.
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0answers
71 views

sounds of polygonal ring chimes of metal

Suppose we have a number of rings, each of them is constructed from some mass of wrought iron or steel: each ring is a polygon, which I would like to suppose is constructed without welding (so they ...
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0answers
24 views

Error in FFT (Sectrum) analyzer Instrument

Recently I performed an experiment on finding the natural frequency of vertical cantilever. I used accelerometer and FFT analyzer instrument for measuring it. First I kept the accelerometer near the ...
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2answers
120 views

Are sinusoidal travelling waves also normal modes of vibration?

According to definition of normal modes, which says if all the different independent parts of a system vibrate at same frequency and their amplitude preserve a fixed ratio then such a motion is a ...
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1answer
43 views

Shouldn't reflection at the boundary interfere with the original wave to not give any wave?

So I have been taking a wave course, and one thing that I don't understand is how does reflection even allows normal modes of vibration. I'll try to explain my confusion: Suppose we have a string ...
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0answers
57 views

Prove from first principles that a guitar string will vibrate at a constant frequency

From experience I am aware that a taught string will generally vibrate with a constant frequency. I wanted to prove this by considering the relation of distance from the resting position, and its ...
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2answers
101 views

Calculating the power of a pneumatic piston vibrator

I am using a pneumatically-driven piston vibrator to compact a tank filled with granular material. The intensity of the vibrator can be regulated by changing the pressure of the pressurized air fed ...
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1answer
52 views

Using two simple pendulums to estimate $g$

I know that using the period expression for a simple pendulum we can have an estimation of the acceleration of gravity $g$. I encountered the following question One way of measuring the terrestrial ...
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3answers
171 views

Vibrating string as a dynamic system

It's known first order dynamical systems had one energy storage (example C, in RC circuits) these systems act as a filter but don't resonate, on the other hand a second order system had two energy-...
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4answers
3k views

If all harmonics are generated by plucking, how does a guitar string produce a pure frequency sound?

A guitar is a plucked instrument and it is played by plucking a string at an off-centre point fixed at two ends. In general, Fourier analysis tells that all harmonics (the resonant frequencies of the ...
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2answers
2k views

Why does a metal block make a shrill sound but not a wooden block upon hammering?

When hammered, a metal block makes a shrill sound but not a wooden block of identical shape. Is it that the wooden block vibrates with lesser frequency than the metal block? If so, why is that? Also ...
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0answers
35 views

Vibrational Question [closed]

A friend recently asked me this question, which I am not even sure how to comprehend... Three masses are arranged at the vertices of an equilateral triangle and are connected by springs along the ...
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2answers
216 views

Human perception of temperature

I had the following thought experiment recently: Suppose we have a vibrating plate for which we can tune the amplitude and frequency of vibration, and imagine we hold a finger against the plate. For ...
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1answer
37 views

Why is the UV absorption band for molecules not a sudden transition?

From what I have read, when a molecule in solution or gas is excited, it does so from ground state, but may gain the energy for vibrational transitions as well. This would lead me to expect that there ...
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2answers
3k views

Can the vibrations from the Earth affect gravitational wave detectors?

I was very interested in gravitational wave detectors and how they work exactly. From what I know they set up two lasers with mirrors set up to cancel each other out. Then if movement is detected from ...
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0answers
48 views

Laser creating weird patterns on screen when reflected from a vibrating membrane

Me and a few friends were doing an experiment today in which we took a membrane stretched over a speaker, and a small mirror in the center of the membrane. We reflected a laser off the mirror on a ...
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2answers
109 views

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
221 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
53 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
214 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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1answer
248 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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1answer
66 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
123 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
308 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
196 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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1answer
79 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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1answer
68 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
37 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
18 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
70 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
81 views

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
162 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
120 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
26 views

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
653 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
116 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
250 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
71 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
638 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
556 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
129 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
41 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
819 views

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:- ...