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Why a wave cannot propagate in a non-elastic medium

We know that wave is a distrubance and carries energy. In this sense let imagine fall of dominoes, which carries disturbance and energy. Here fall of dominoes is non-elastic and we can see that wave propagates. Can I call it as a wave?

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  • $\begingroup$ I hope by "waves" you mean "mechanical waves". "Non-mechanical waves" don't need a material medium at all. $\endgroup$
    – Vishnu
    Commented Apr 1, 2020 at 11:18
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    $\begingroup$ @GuruVishnu, it's more accurate to say that some thinkers conceive of space as being something other than a medium, or performing some role in electromagnetic theory which is fundamentally different from that of a medium. In practice, regions of free space are treated as having properties like mediums, and treating free space as a medium introduces no complications. $\endgroup$
    – Steve
    Commented Apr 1, 2020 at 13:03
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    $\begingroup$ Teja, it's not so much that waves cannot propagate in non-elastic mediums, it's that non-elastic mediums don't exist. If they did exist, they would be perfectly capable of transmitting waves. $\endgroup$
    – Steve
    Commented Apr 1, 2020 at 13:08
  • $\begingroup$ See physics.stackexchange.com/q/524377/45664 the answer to your question is there. $\endgroup$
    – user45664
    Commented Apr 1, 2020 at 17:37

2 Answers 2

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Waves can propagate in an inelastic medium, and the fall of dominoes is a wave. So when people say that a wave can't travel in a non-elastic medium can't, this statement applies to particular kind of waves.

When talking about waves one often means perturbations that are periodic in space and periodic in time at every point. This is not the case in an inelastic medium, where due to damping, such a wave would decay.

Yet, for the case of dominoes such terms as solitary wave, shock wave or soliton could be quite appropriate - the kind of single "waves" associated with explosions, tsunami, propagation of cracks, etc.

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    $\begingroup$ Non periodic waves such as an impulse, $\delta(x-ct)$, are considered waves since they satisfy the wave equation. $\endgroup$
    – user45664
    Commented Apr 1, 2020 at 17:24
  • $\begingroup$ I improved it. Thanks! $\endgroup$
    – Roger V.
    Commented Apr 1, 2020 at 18:33
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I think it goes like this. A mechanical wave is indeed a periodic perturbation the particles of the medium through which it travels, and if the medium is non-elastic, as most media are, then energy will be lost at each 'passing on' of the energy from one particle to the next. This is the cause of the attenuation of mechanical waves over distance. The more elastic the medium, the farther the wave will travel. A wave can travel in a non-elastic medium, but not very far. Although it is not quite the same thing, consider the speed of sound in air (331 m.s-1), water (1,403 m.s-1), ice (3,838 m.s-1), iron (5,120 m.s-1) & diamond (~12,000 m.s-1). As we progress through that list, the medium becomes more elastic(/brittle), and sound will travel farther.

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