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57

If there were only one prong (imagine holding a metal rod in your hand), then the oscillation energy of the prong would quickly be dissipated by its contact with your hand. On the other hand, a fork with two prongs oscillates in such a way that the point of contact with your hand does not move much due to the oscillation of the fork. This causes the ...


50

In order to properly understand this without any unnecessary "controversy", let's break the whole process of sound generation and perception into 5 important, but completely separate parts. We'll then proceed to explain each part using a few different examples and pieces of derivative logic: Vibration of the vocal folds Transmission of energy from vocal ...


45

I am by no means an expert in tuning fork design, but here are some physical considerations: Different designs may have different "purities," but don't take this too far. It is certainly possible to tune to something not a pure tone; after all, orchestras usually tune to instruments, not tuning forks. Whatever mode(s) you want to excite, you don't want to ...


27

The reason for having two prongs is that they oscillate in antiphase. That is, instead of both moving to the left, then both moving to the right, and so on, they oscillate "in and out" - they move towards each other then move away from each other, then towards, etc. That means that the bit you hold doesn't vibrate at all, even though the prongs do. You ...


21

Q. How do two coupled vibrating prongs isolate a single frequency? howstuffworks.com has an article on How Tuning Forks Work The way a tuning fork's vibrations interact with the surrounding air is what causes sound to form. When a tuning fork's tines are moving away from one another, it pushes surrounding air molecules together, forming small, ...


13

There seem to be a lot of human body mechanical models, such as this one: As for applications, I have heard that sub-audio frequency vibrations have been considered as nonlethal weapons for riot control.


12

The car is behaving like a closed pipe, so you get a resonance set up. There's a Wikipedia article here, but for once the Wikipedia article isn't that great, so there's another better article here. I imagine you (like most of us) will at some point have discovered you can make a sound by blowing across the top of an opened bottle, and it's the same thing ...


7

It would depend on damping effects being taken into account or not. Invoking Newton's 2nd Law of motion, a differential equation for the motion of a damped harmonic oscillator can be written (including an external, sinusoidal driving force term): $m\frac{d^2x}{dt^2}+2m\xi\omega_0\frac{dx}{dt}+m\omega_0^2x=F_0\sin\left(\omega t\right)$ Where $m$ is the ...


7

What you are seeing on the square plate are the resonant modes of the structure. Each of these modes has a particular frequency associated with it, and is rung up when the plate is driven at that frequency. These resonant modes act like standing waves on a string: where some parts of the plate are moving a lot while other parts are standing still. The sand ...


6

The first generation of elementary particles are by observation not composite and therefore not seen to decay. They are shown in this table of the standard model of particle physics in column I. The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column and the Higgs boson in the fifth. All ...


6

First: what frequency should you hit? There are many, many different factors at play in determining the natural frequency of an object I know from experience. These are (not limited to): Thickness, density, elasticity modulus (you'll need two of those, e.g. Young's Modulus and Poisson Ratio), and of course shape. I'm not aware of any papers publishing a ...


6

A resonance (in the particle physics or related physics sense) and an unstable particle is exactly the same thing. The object has some complex mass and the imaginary part determines the decay width (and decay rate). But these two terms describe different aspects of the same thing. "A particle" refers to the object, the particle species (in your URL's case, ...


5

If we look at the sonic boom as a $\delta$-function, where we have a really loud sound for a really short time, then it will be able to excite all frequencies at the same way. You can actually compute this by showing that $$ \delta(t)=\frac{1}{2\pi}\sum_n e^{int},$$ which show how the $\delta$-function is actually composed of all frequencies. Then it's ...


5

Does that mean when I apply a voltage, the current will be infinite large? No, not even in the context of ideal circuit theory. It's a bit subtle since we're using phasor voltages and currents and that requires a couple of assumptions to hold in order to be valid. When those assumptions don't hold, we have to see what the 'infinity' (division by ...


5

Re question 1: when you learn this stuff in school you usually simplify the system by modelling it as a simple harmonic oscillator so the amplitude of the system will be given by some equation like: $$ A(t) = A_0 e^{i\omega_0 t} $$ where $\omega_0$ is the natural frequency of oscillation. Typically you study what happens if you apply a force that also ...


5

It is caused by standing waves in the container. You get, as a result, harmonics. There are overtones occurring for a fixed frequency. The changing sound is because a water filled container is like the half open model in the picture below. As the water level rises, the length of the tube decreases. This would lead to a change in the frequency of standing ...


4

I have just noticed the question. Indeed, the body does have very clear resonances. Nature has prioritised speed of movement over stability so limbs are underdamped and naturally resonant. It is likely that many rhythmic movements occur at the resonant frequency of the body parts involved (rather similar to the oscillation of some insect wings). A ...


4

In physics, resonance is the tendency of a system to oscillate with greater amplitude at some frequencies than at others. Frequencies at which the response amplitude is a relative maximum are known as the system's resonant frequencies, or resonance frequencies. (Copied from Wikipedia: Resonance.) The Fano resonance and the Feshbach resonance are the same ...


4

In an experiment in which particles are collided, a resonance is a large peak in a cross section (rate at which a process occurs) when plotted against the energy of the incoming particles. For example, when LEP collided electrons with positrons, they saw a resonance when the energy of the incoming particles equalled the mass of the $Z$-boson. Resonances ...


4

The oscillator frequency $\omega$ says nothing about the actual oscillator phase. Let us suppose that your oscillator oscillates freely like this: $$x(t) = A_0\cdot\cos(\omega t + \phi_0),\; t<0.$$ At $t=0$ it has a phase $\phi_0$. Depending on its value the oscillator can be moving forward or backward with some velocity. If you switch your external force ...


4

Any physics-oriented FEM solver should do this. I have only done it with COMSOL, which is proprietary and expensive, but searching Ubuntu's repository of free software turns up at least two promising candidates: Elmer and FreeFEM. I'm trying out Elmer now. http://www.csc.fi/english/pages/elmer http://en.wikipedia.org/wiki/Elmer_FEM_solver This example ...


4

No, because in a vacuum, there is no way for the two tuning forks (I think you meant this, rather than pendulums) to communicate. The reason a second tuning fork with the same resonance frequency will begin resonating is because, physically, sound waves are hitting it at its natural frequency. Sound waves travel in a medium, so in a vacuum, there's nothing ...


4

The Moon moves away about four inches a year on Earth, 15 while the Earth's rotation is slowing down, which will in the distant future total solar eclipses occur stop the moon not having sufficient size to cover the solar disk. In theory, this separation should continue until the Moon takes 47 days to complete one orbit around our planet at which our planet ...


4

Vibrations begin to resonate together into sound waves we can hear. We can make the sounds loud or soft depending on how much pressure we place on finger. The pitch of the sound can also be changed by adjusting the amount of water in the glass.As you rub your finger on the rim, your finger first sticks to the glass and then slides. This stick and slide ...


4

From here, how do I define the "resonance"? At resonance, the energy flow from the driving source is unidirectional, i.e., the system absorbs power over the entire cycle. When $\Omega = \omega_0$, we have $$\phi(t) = \frac{A}{2\beta \omega_0}\sin\omega_0 t$$ thus $$\dot \phi(t) = \frac{A}{2\beta}\cos\omega_0 t$$ The power $P$ per unit mass ...


3

So there is not an easy way - I had to grind out all the algebra. Starting with $$\nabla^2 E +k^2E = 0$$ The Electric field forms are $$E_r = P_n^0(cos\theta)[\frac{A_n j_n(k r)}{k r} + \frac {B_n y_n(k r)}{k r}]$$ $$E_\phi = P_n^1(cos\theta)[C_n j_n(k r) + D_n y_n(k r)]$$ Using $\nabla \cdot E = 0$ and the symmetry over $\phi$ I find $$E_\theta = -\frac ...


3

I don't consider myself an expert in MRI, but let me try (since nobody else has stepped up in the last hour...) You are right with your first assertion: the spin precesses about the B vector (this is why you get resonance in the first place). However, on average there is a net component of the magnetic moment aligned with the B field. This is what gives ...


3

Several reasons why this is not a great idea: 1) signal to noise ratio scales with field strength: 1.5T is considered a reasonable number although it is possible to get diagnostic images in some situations with lower fields. 2) inductance of coil capable of producing such large fields - try computing the energy stored! 3) during ramping of the magnet, you ...



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