1
$\begingroup$

I'm finally closing some gaps in sound waves, so forgive me for lots of questions.

In metal, it's said sound travels fastest. The reason is molecules are tightly packed(more dense) in metals than in air lets say, and collisions with each other will be fast as each molecule doesn't have to travel long before it collides with another one, hence it travels faster. Though, I wonder even though it will be faster, we should have disadvantage here which is the signal created by source won't be much weak than it would be in air. My logical thinking is since molecules are tightly packed, it will be harder to transfer energy from particle to next particle(more tightly packed, harder to vibrate the same frequency as created by source).

So even though sound travels fast in metal, it should give us weaker signal in the end than in air. Would this logical thinking be correct somehow?

Improve this question
$\endgroup$
2
  • 1
    $\begingroup$ The intensity is inversely proportional to the density of the medium and speed of sound in the medium, so you have the right idea. If you looked up the equation that relates all these, you can actually calculate how much the difference is between a certain metal, and air. $\endgroup$
    – joseph h
    Commented Jun 3, 2023 at 1:41
  • $\begingroup$ There is no collisions in solids when sound propagates, the perturbation affects only the metallic bonds and the lattice vibrates : acoustic phonon. An ideal metal consists of a perfectly ordered lattice, where such a perturbation has a long range propagation. Once a perturbation is created, a metal relaxes and the signal is weakened only in presence of impurities. $\endgroup$
    – M06-2x
    Commented Jun 3, 2023 at 4:30

2 Answers 2

Reset to default
2
$\begingroup$

It's important to understand that the speed of sound in a medium is proportional to the allowed wavelengths within that medium. That is, a medium with a higher speed of sound will admit shorter wavelengths because the particles can transmit vibrations more quickly.

Shorter wavelengths tend to encounter more internal friction and viscosity, resulting in absorption as they travel through a given medium. This results in them experiencing more damping per unit distance than longer wavelengths do.

Improve this answer
$\endgroup$
2
  • $\begingroup$ Transmitting vibrations will occur faster but transfering energy will be less from particle to particle since they are tighly packed with a bigger mass. But I wonder about absorption. Isnt vibration the cause of absorption ? If so how are they different ? $\endgroup$
    – Giorgi
    Commented Jun 3, 2023 at 8:24
  • $\begingroup$ Mainly, if absorption is different thing, when particles collide, some energy should go into absorption(which wont cause more vibration of particle 2) and it will directly heat the molecule. But heat and kinetic energy is related so if it was transformed into heat, it implicitly means it is again transformed into KE of particle 2. So why absorption and vibration different things ? $\endgroup$
    – Giorgi
    Commented Jun 3, 2023 at 8:41
2
$\begingroup$

Your intuition is insightful. In fact to factors enter at play: the speed of sound in the medium and the attenuation of sound in the medium.

Speed of Sound: As you correctly noted, the speed of sound is much higher in metals than in air. This is because sound waves are mechanical waves and require a medium to propagate. In solids, where atoms/molecules are densely packed, sound waves can propagate faster because neighboring atoms/molecules can quickly transmit the wave's energy.

Attenuation of Sound: This is where things become interesting. Attenuation refers to how much the sound wave diminishes (loses energy or amplitude) as it travels. The attenuation of sound in a medium depends on several factors, including the frequency of the sound, the properties of the medium (like its density and elasticity), and the presence of any obstacles or defects in the medium.

Now, to your question: Would sound get weaker in metal faster than in air over the same distance?

The answer is not straightforward because it depends on the specific conditions, especially the frequency of the sound and the specific properties of the metal and the air. Generally, at normal frequencies, the attenuation of sound is less in air than in many metals, so sound can indeed travel farther in air without losing as much of its energy. This is due in part to the mechanisms of sound attenuation in metals, which include scattering of the sound waves from defects in the metal and thermal conduction, both of which can cause the sound wave to lose energy. In solids, sound waves interact with the lattice structure of the solid, which can cause scattering and conversion of sound energy into other forms, leading to attenuation. Gases, being less dense and less structured, usually provide less resistance to the propagation of sound waves, leading to lower attenuation. However, materials science is pretty advanced and perhaps there is some way to create a given metal that would resonate and don't damp certain frequencies.

As an aside note about the weakness you would have in metal, note that even though sound might be attenuated more in metal than in air over a given distance, the sound wave can still carry more information or be more "recognizable" when it arrives because of the higher speed of sound in metal, which can preserve the shape of the wave better than the slower speed of sound in air.

In conclusion, while the speed of sound in metals is higher, the attenuation can also be higher, which means that sound can lose energy more quickly in metals than in air. But the specific outcomes can depend on many factors and are not easy to predict without more detailed information.

If the answer is longer than necessary I invite the community to actively change it.

Improve this answer
$\endgroup$
2
  • $\begingroup$ Thanks for the great answer. Though I was more curious about why energy lost could be higher in metals. My logic said: “ since molecules are tightly packed, it will be harder to transfer energy from particle to next particle(more tightly packed, harder to vibrate it with the same frequency as created by source”. But you dont mention it . particles will collide more often in metals, is the cause of more energy lost into heat but also as I said, tigher packed must mean the bond is stronger mass of particles so vibrating it with same frequency wont be possible. Thoughs ? $\endgroup$
    – Giorgi
    Commented Jun 3, 2023 at 7:50
  • $\begingroup$ I hope this helps a little. Energy is converted into heat due to the friction between these particles, a process known as damping or absorption. This loss is much less in air due to its lower density and the weaker forces between air molecules.There are other possible causes for loss of energy too: Impedance Mismatch, Internal Friction, and Scattering. As a note, damping is a broader term that includes internal friction, but it can also include other forms of energy dissipation. For instance, viscous resistance. Sorry for the short answer, I cannot write many characters. $\endgroup$
    – andres gomez
    Commented Jun 4, 2023 at 17:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.