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202
votes
4answers
36k views

Can I compute the mass of a coin based on the sound of its fall?

Other day, I bumped my bookshelf and a coin fell down. This gave me an idea. Is it possible to compute the mass of a coin, based on the sound emitted when it falls? I think that there should be a ...
74
votes
6answers
6k views

Why do tuning forks have two prongs?

I believe the purpose of a tuning fork is to produce a single pure frequency of vibration. How do two coupled vibrating prongs isolate a single frequency? Is it possible to produce the same effect ...
12
votes
2answers
401 views

Why does vibration loosen screws?

I am trying to figure out why vibrations (say, from an engine) loosen screws. It seems to me that there is evident symmetry between loosening and tightening a screw. I am wondering what breaks this ...
9
votes
1answer
889 views

Theory behind patterns formed on Chladni plates?

In this video of vibrating Chladni plates we can see small sand particles align themselves into different interesting patterns (also shown in the image below) which correspond to some particular ...
8
votes
2answers
102 views

Picking up audio using high speed video?

In the movie Eagle Eye, ARIIA (an intelligence-gathering supercomputer/AI) picks up audio using video recording of the vibrations in a coffee cup. How close is this to reality? I have see it done ...
6
votes
5answers
241 views

Why do harmonics occur when you pluck a string?

When you energise a taut string, the following resonant modes of vibration occur: Plotting on the frequency domain, you can see their corresponding frequencies: But what is the underlying ...
5
votes
0answers
85 views

To what degree does guitar construction affects the vibration of the strings?

There's an old debate going on in the guitar community about how much does wood choice and body shape affect the sound of an electric guitar. No one denies that there's a difference acoustically (how ...
5
votes
1answer
235 views

Vibrational anharmonic coupling and noise-induced spontaneous symmetry breaking in a hexagonal finite mechanical lattice

Happy holidays, everyone! The following is part question, part visual gallery, and part classical mechanics problem. Inspired by snow over the weekend I began simulating the vibrations of the ...
5
votes
0answers
192 views

Physical meaning of Laplace-Beltrami eigenfunctions?

The eigenfunctions of Laplace-Beltrami operator are often used as the basis of functions defined on some manifolds. It seems that there is some kind of connection between eigen analysis of ...
4
votes
2answers
351 views

Why sound does not heat up the air?

Both thermal energy and air are propagated through vibration of particles so why sound does not heat up the air e.g loud musical instrument does not generate much heat ?
4
votes
2answers
71 views

Do Baryons have Quantized Vibrational and Rotational States?

Given that baryons are not point particles but are composed of three quarks, are there quantized vibrational and rotational states analogous to those of molecules? If not why not, and if so are ...
4
votes
4answers
383 views

Understanding Heat

Heat or thermal energy as understood is nothing but motion of molecules of the matter. If the molecules are tightly bound (in case of solids), it is to-and-fro molecular vibrations, otherwise it is ...
4
votes
2answers
382 views

Frequency of touch, taste, and scent [closed]

So I was thinking about sound - and how anything below 20Hz is basically inaudible to humans (because it is too low of a frequency to be recognized), as well as anything above around 20KHz (because it ...
4
votes
3answers
651 views

Is photon emission possible without electrons changing energy levels?

Does molecular vibrational transition and consequent emission of infrared radiation involve electrons changing energy level? In wikipedia, about vibronic transitions it says "Most processes leading to ...
4
votes
1answer
196 views

Equations of motion of displacement field

We have an action: $$S[\boldsymbol{u}] = \frac{1}{2} \int dt \int d^3x \left\{ \mu (\frac{\partial u_{i}}{\partial t})^{2} - \nu (u_{ii})^{2} - \rho(u_{ij})^{2}\right\} $$ Where $u_{ij} = ...
3
votes
1answer
538 views

Phenomena which are incorrectly declared as resonance phenomena?

In standard college physics text books, high-school books and popular level physics books, the collapse of the Tacoma Narrows Bridge is often taken as an example of resonance. However a more detailed ...
3
votes
3answers
91 views

Difference between sound and heat at particle level

If heat (or thermal energy) are vibrations of particles and sound is a wave that is propagated through medium e.g vibration of air particles, what indicates if vibration of particles will be perceived ...
3
votes
1answer
59 views

Moments of vibrating string

I have to calculate first 10 moments for vibrating string with damping, but I don't know how to do it. I read about moments and in definition they mention linear system $$x'=Ax+Bu, \qquad y=Cx$$ with ...
3
votes
3answers
1k views

Design of a common table fan

A few questions about the design of a common table fan, such as below. Does the round disc (silver in the image) in front of the blades serve any functional purpose? Does the metal casing around the ...
3
votes
0answers
47 views

Finding the components of the tensor for potential and kinetic energy

I have a rather poor understanding of what a tensor is, but enough to apply it to the biggest part of the classical mechanics I'm studying. However, I've run into a small problem while studying "Free ...
3
votes
0answers
78 views

Sound - for purposes of vibration

What is the best way to distribute noise from more than one source (I'm envisioning a system with many), within a dome, with the ground as its primary target, at optimal frequencies and volumes to ...
2
votes
2answers
179 views

“Magic” Speed to Drive Over a Speed Bump: Myth or Reality?

A somewhat controversial aspect of speed bumps (sleeping policemen for those in the UK) is that they arguably cause more loss of life than they prevent by acting as a hindrance to emergency response ...
2
votes
1answer
75 views

What happens to the energy?

if we make a bell ring in a vacuum room for 5 mins. And then open the door, will be able to hear the sound? If no sounds vibrations are emitted to the environment what happens to the energy that ...
2
votes
2answers
209 views

Can the vibrational energy of a engine be used to increase efficiency?

In whole mechanics, we never talk about wasted vibrational energy! As we see in our daily life, a lot of energy is wasted as vibrational energy in every engine, for example as we fire our car's ...
2
votes
2answers
201 views

Stick and slip motion: mass and spring inside a box model

I am trying to determine a set of differential equation which can describe the motion of a mechanical system as below. Here, at the bottom we have a plate, and a box on top of it. Inside the box, ...
2
votes
1answer
429 views

Question about the quantization of lattice vibration (phonons)

In my syllabus about solid state physics they state that lattice vibration is quantized, analogous to the harmonic oscillator: $$E = (n+\frac{1}{2})\hbar\omega$$ So the lattice vibration has ...
2
votes
1answer
36 views

Forced vibration

Let's consider a spring which is subjected to forced vibrations: $$ F = F_0 \cos(\omega t) $$ Is the resonance frequancy $\omega_0$ of the spring dependent on the amplitude $F_0$? I ask this ...
2
votes
1answer
355 views

Spring system - 3 DoF system and its properties while changing stiffness

I was given the attached 3 degree of freedom spring system with the purpose of analyzing it. I came up with the following equation of motion and then I ran Matlab to calculate the corresponding ...
2
votes
2answers
618 views

Orthogonality of modes

I want to know what it exactly means when it is said the modes of vibration are Orthogonal.I understand what it means mathematically but what is its physical interpretation?
2
votes
0answers
46 views

De-excitation and vibrational frequency

By utilising energetic beams of particles it is possible to set atomic nuclei into vibration. For a certain nucleus the subsequent de-excitation results in the emission of photons of energy $1$ $MeV$. ...
2
votes
0answers
125 views

Modal analysis with aerodynamic damping

I'm using modal decomposition to predict the steady state response of a beam structure to harmonic loading. The structure itself is very lightly damped, but we know from experiments that the ...
2
votes
0answers
432 views

Chladni Plate Mathematics

I am a high school student doing an IB Extended Essay investigation concerning the resonant frequencies of Chladni plates of differing materials and sizes. Would someone please explain the definition ...
1
vote
3answers
285 views

Does the speed at which sound travel depend on the volume (amplitude) of the sound?

Lets say you have a plank is you hit it once and get t time if you hit is 2x as hard will it travel t/2? will it be the same or will it travel only slightly faster?
1
vote
4answers
163 views

How come vibrations?

We all know that sound sensation is produced only when sound waves reach upto us. We all know that sound waves are disturbances propagating in air, Vibration is necessary for the generation of sound, ...
1
vote
1answer
55 views

The inverse square law of sound through solids?

We all know about the inverse square law of sound. In short the power of the wave will get evenly spread on an ever increasing spherical expansion and this will dissipate the power of the wave at a ...
1
vote
1answer
119 views

Why does a minor vertical vibration cause my coffee to spill?

When I walk my kid sometimes I put a cut of coffee in a cupholder attached to the stroller. When I push the stroller over a brick pavement it seems to vibrate vertically. That is enough for the coffee ...
1
vote
1answer
500 views

Resonance and Natural Vibrations in Vacuum

In my Physics textbook, it says that if two pendulums of the same natural frequency are placed next to each other and if one is set into vibration, the other starts resonating and when the first one ...
1
vote
1answer
38 views

Why would a screen(with touch controls) in a vibrating environment be readable if its refresh rate is dynamically matched with vibrations?

So, I was reading about this Dragon V2 and it has got touch controlled screens, but screen might be unreadable for pilots because of engine vibrations and whatnot. I came across this comment on ...
1
vote
1answer
62 views

Two coffee beans in a cup of water + vibrations = gravity? [duplicate]

If you float two coffee beans in a cup of water that is being vibrated by your subwoofer (go to a sin wave generator online), the two beans will either be attracted to the sides of the cup or if ...
1
vote
1answer
106 views

Spring Damper System for a Vibrating Motor

Good day people of SE I have a friend that has a final year project and is stuck. He has a motor with a small weight at the end of the shaft that causes vibrations. This motor is on a thin plate. ...
1
vote
1answer
136 views

Does the frequency of a vibrating substance like a string depend on its properties or simply depend on the agent which vibrates the string?

We know that if someone vibrates a substance like a string, the string oscillates with its natural frequency. But I think the frequency depends on the rate the agent like a man's hand does vibration ...
1
vote
1answer
397 views

Why do we need hard steel balls to produce an unusual ‘chirping’ sound?

When two hard steel balls, or similar, are brought gently into contact with each other, an unusual ‘chirping’ sound may be produced.why do we need this material or shape to produce that sound?
1
vote
1answer
83 views

Duhamel formula for propagators

Let $\dot{z} = A(t)z + b(t)$ with $ z(t) \in \mathbb{R}^n$ and $A(t)$ be a linear map from $\mathbb{R}^n \rightarrow \mathbb{R}^n$. A propagator is also a linear map $P(t,s):$ $\mathbb{R}^n ...
1
vote
2answers
132 views

With the phone Vibration why the whole bed vibrates

While we are lying on the bed and there is a phone placed somewhere on the bed, when the phone vibrates we can feel the vibration all over the bed, but in the scenario when we are lying on the floor ...
1
vote
2answers
19 views

What is the meaning of pre-tension for a stiff membrane?

On one hand, I know that the tighter a drum head is stretched, the higher its natural frequencies. This relation is given by: $$f_{ij}=\frac{k_{ij}}{2\pi R}\sqrt{\frac{T_0}{h\rho}}$$ where $k_{ij}$ ...
1
vote
1answer
42 views

Vibration in a broken cylinder

The physics S.E. may be wrong for this question, but I wonder what happens to a vibration in broken, cracked, or otherwise damaged cylinder. Say you have a 1 meter long steel cylinder, you break it in ...
1
vote
1answer
225 views

How do I recover the 1D wave equation from the Lagrangian?

Consider small displacements, $y(x,t)$, of an element of a string (circled in red and shown below) from equilibrium. The force balance in the vertical direction yields: $$+\uparrow \Sigma F: ...
1
vote
2answers
611 views

Why is simple harmonic motion called so?

Is the motion of a simple pendulum, a simple harmonic motion? It stops vibrating after sometime.
1
vote
1answer
219 views

What is actually a resonating vibration and resonance?

What is actually a resonating vibration and resonance? I have searched many books and made Google search too but couldn't understand it clearly.
1
vote
0answers
15 views

Can an axisymmetric solution produce antisymmetric eigenfunctions?

I'm solving a vibrating membrane. In order to simplify my calculations, it's tempting to assume axisymmetric behaviour. If I solve an axisymmetric problem, am I going to lose all the antisymmetric ...