This is a question about mechanical waves. As i understand it, there can be many different types of mechanical waves, but its is not allways necessary to actually make a physically motion of one harmonic oscillator (a partical, or a part of the medium that the mechanic waves travels throw) to start or hinder a mechanical wave. The force spreads throw the medium even if the physical motion of the harmonic oscillators is somehow hinderd. And the physical motion of the mechanical wave will come back once the obstacle have been passed. Let my me try to further explain what i mean with a picture !-----! -> this is the wave moving in the direction of the arrow ___! !______0000000000________ the zeros 000 are obstacles !----- -! -> this is what will happen ___0000000__ __! !______ Am i right? And why does this happen? Is it because the force or power traveling throw the medium treavels between the atoms and molecules of the harmonic oscillators once the actuall motion of the oscillators in not possible?