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A piece of iron has ferromagnetic domains: iron and other ferromagnets are often found in an "unmagnetized" state. The reason for this is that a bulk piece of ferromagnetic material is divided into tiny regions called magnetic domains[13] (also known as Weiss domains). Within each domain, the spins are aligned, but (if the bulk material is in its lowest ...

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You typically have one position and one velocity variable per oscillator. The equation of motion of mass $i$ is $m_ix_i''=k_ix_i+$coupling terms. If the forces from the coupling terms are small, the frequencies do not change much. If the coupling is large, you will have as many modes as oscillators, but the frequencies can be anything. You wind up finding ...

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The Q of a system tells you over what range of frequencies it can be excited, and how much "amplification" you get at resonance. If you have a system with a high Q (narrow bandwidth) and you drive it with an off-resonance frequency, you will get barely any response. If instead you sweep the frequencies, then at the time you hit the frequency "on the nose" ...

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Generally speaking mechanical structures, if they 'ring' at all, will ring at frequencies determined by the properties of stiffness (elasticity) and mass. The frequency in most cases increases with increasing stiffness, but decreases with increase in mass. Buildings have considerable stiffness, but not necessarily that large considering the relative mass ...

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In order to excite a resonance in something, you need to produce oscillations that add coherently, or in phase. This means that when you vibrate on object, you will want the reflections of the vibration to add with the new vibrations that are coming in. These reflections will take time to get from one end of the object to the other given the finite speed ...

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Keep in mind that the bold text isn't a derivation, its a way to qualitatively understand, so it's going to be very very unconvincing. Instead of imaging that you are trying to compute a number imagine you are trying to estimate it by a factor of 10 or 100 or even a factor of 1000 or more. That's how unconvincing it will be. So. At equilibrium amplitudes, ...

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