The speed of a wave depends on what the wave is traveling through. Two factors affect the sound speed: elasticity and inertia.


[am4show have=’p9;p58;’ guest_error=’Guest error message’ user_error=’User error message’ ]



Sound waves traveling through steel, a material that is rigid, will not deform like it would if it were traveling through rubber. The atoms that make up steel are bound tightly together, so when a force tries to move them around or pry them apart, it’s very hard to do. Steel has a high modulus of elasticity, which means that it’s rigid (at least in the solid state). Materials usually have the highest modulus of elasticity when they are in their solid state and least in the gaseous state, which means that longitudinal sound waves will travel faster in solids than liquids and gases.


Sound travels faster in less dense materials, so it will travel faster in helium than it will in air for example (ever used a balloon to change the pitch of your voice?) The greater the density of the individual particles, the less responsive they are to interacting with their neighboring particles, so the wave travels slower. More massive particles like air molecules take more energy to move around than lighter particles like helium molecules.


If you have to choose between inertial and elastic effects having the greatest influence on the speed of a wave, the elastic effects have a greater impact, so the speed of a wave in solids is generally faster than through liquid, and sound waves traveling through liquids are faster than through gases.


Click here to go to next lesson on Lightning and Thunder.

[/am4show]


Have a question ?

Tell us what you're thinking...

Comments

2 Responses to “Elasticity and Inertia”

  1. Aurora Lipper says:

    At 2:00, the video is discussing gasses. Since the molecules in helium are lighter than the nitrogen and oxygen in air, helium has less resistance to vibration. So, when considering helium or air at the same temperature and pressure, sound travels faster in helium. However in liquids and solids, sound travels faster in denser materials.

  2. herdingkittens says:

    In the video, at 2:00, it says that sound travels faster in less dense materials, but earlier in the course it said that sound travels faster in denser materials, like rock.