Question

why does sound travel faster in less dense objects?

Answer 1

It takes more energy to make large molecules vibrate than it does to make smaller molecules vibrate. Thus, soundwill travel at a slower rate in thedenser object. ... Sound moves fasterthrough denser air because the molecules are closer together in denseair and sound can be more easily passed on.

Answer 2

hello Frnd..*_*


I suspect by “denser” you mean material that is more closely packed. That often leads to a stiffer material - one with a higher bulk modulus. But packing atoms closer together can also increase the mass density of the material - and that leads to a lower speed of mechanical wave propagation through the material. So it is more complicated than just considering the density of the material. So we should separate those two ideas in describing what controls the speed of sound through a material.

The speed of sound in materials depends on both the compressibility of the material as well as its mass density. Higher compressibilities - that is, materials that can be more easily compressed - correspond to less rigid interactions between the atoms of the material and hence tend to have lower mechanical wave speeds. And materials with higher mass densities also tend to have lower wave speeds. Or said differently, a stiffer, less compressible material will tend to have a higher speed of sound, whereas higher mass density materials will tend to have a lower speed of sound. And mass density depends on both the masses of the atoms, how close together they are, and how they are arranged (i.e., their atomic structure). The reason the speed of sound in water is much greater than the speed of sound in air is because the compressibility of water is so low even though it has such a high mass density compared to air.

A conceptual model to help us think about this is a long chain of masses connected by springs - and to think about the propagation of a disturbance if one end of the chain is jiggled in some way. The stiffer the springs, the more quickly the vibration of one mass will affect a neighboring mass. So with very stiff springs, a vibration can be sent rapidly down the chain. On the other hand, the heavier the masses - or the more masses per unit length, the more sluggishly they will respond to the forces the springs exert, and the slower the response, the more time it takes to propagate the disturbance along the chain of springs and masses. So one would expect higher wave propagation speeds through a system with stiffer springs and lighter masses - or fewer masses per unit length. (Formally, the speed of sound through a material is equal to the square root of the bulk modulus divided by the mass density. But the above should give the idea.)

For example, lead, which is quite dense, has a relatively low wave propagation speed because it is a relatively soft material even though it has a high mass density. Aluminum has a fairly high wave speed because it is a stiffer metal with a fairly low mass density. Diamond has a very high wave propagation speed because the covalent bonds of the carbon atoms are very rigid, and even though the diamond crystal structure places a lot of carbon atoms close together, the carbon atoms themselves are low mass - so the rigidity of those bonds creates a high wave speed.

I hope that gives a somewhat clearer picture of what controls the speed of sound in materials.