Why does sound travel faster in helium that is lighter than air but also travels faster in water that is more dense than air?
In: Physics
If you think about it this way. Air is mostly nitrogen and oxygen which are both heavier elements than helium. So getting air to move a certain way is going to take more energy to get things going and will also be slower in doing it. It’s exactly like if you push on a car, it’s not going to move much but if you push on a ball it’ll roll away from you easily.
For water, the atoms are all packed in together and all but touching. The moment you hit one water molecule, the energy quickly transfers to the next because it doesn’t have far to go to do it.
For another example, think about a game of billiards. Except at the start you line all the balls up in a straight row touching each other down the length of the table. Hit one end of the row and the ball at the other end pops off almost immediately. That’s how water do.
Now put an inch or two between each of the balls in that same kind of line and when you smack one end it takes a few seconds before the ball at the other end starts to roll. That’s how gas do. (In this case water vapor)
If you replaced the billiard balls with say squash balls or tennis balls, it should take a little less time for the far end to get moving because there’s less momentum to overcome for each ball in the chain. That’s how it looks for any gas lighter than water in gas form. Which is similar to how helium is “lighter” (less massive) than air.
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