Density & the Speed of Sound

Recall that a medium can be a solid, liquid, or a gas.
In which medium, to you think a mechanical wave travels fastest?

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​A wave travels more quickly through denser materials, so it travels faster through solids, than it would through a liquid or gas.


**The more tightly packed the particles, the greater the density.

​Particle arrangement and motion

In a solid, particles are packed tightly together so they don't move much, but are dense. The electrons of each particle are constantly in motion, giving the atoms a small vibration, but they are fixed in their position.

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Solids have a definite shape, as well as mass and volume, and do not conform to the shape of the container in which they are placed. 

In a liquid, the particles are more loosely packed than in a solid, but closely enough that it is not easily compressible.

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The particles are able to flow around each other, giving the liquid an indefinite shape. Therefore, the liquid will conform to the shape of its container.

In a gas, the particles have a great deal of space between them, so they move easily, and have high kinetic energy (energy of movement).

Sound waves travels slowest in a gas.

Rationale: In a gas, the particles are spread out far apart so it doesn't have as many particles to support it as it does in a solid (tightly packed particles) or a liquid (looser particles).

​Rationale:

The chart shows the speed that sound travels in the 6 substances.

If I know that sound travels fastest in denser materials, then I know that the material with the fastest speed must have the greatest density.

​According to the chart, the speed of sound in water (1498m/s) is faster than the speed of sound in air (343m/s), so you can rule out any choices that say the speed of sound in water is slower than in air. **Rule out the 1st 2 in this example.

Rule out!
**explanation above

Rule out!
**explanation above

Speed of sound faster- true

False part- water molecules are more dense- not less.

Closer particles means more dense.

Faster in water.- Y
molecules closer- Y
more dense- Y

Correct

Sound Waves (Mechanical Waves)

Sound waves are mechanical waves, meaning they need a medium to travel. The more tightly packed the particles of the medium are (more dense), the faster the wave can travel.

**If sound is traveling though the air (a gas), it will slow down when it hits water (a liquid). This causes the sound wave to refract. (bend)