Why doesn't the Earth at the equator experience a sonic boom?

[Ibix]

could you expound this please?

The point, I think, is that the underlying problem you have with the atmosphere is that it's not nailed down, but rotates with the Earth anyway. The same is true of the oceans. So if you personally don't have the same problem with the oceans as with the air, there's a crack in your thinking that you might be able to lever open and gain insight.

The basic answer is friction. If the atmosphere were, in bulk, rotating at a different rate from the ground, each collision between an air atom and a ground atom would tend to result in the average rotation rates getting closer together. There would be a transfer of energy from the faster rotating part to the slower one. The same applies to the ocean.

As others have noted, a stationary atmosphere and a spinning Earth is not a realistic model of atmosphere formation. But this does explain why co-rotating Earth and atmosphere is stable. If some combination of events (billions upon billions of carefully coordinated and aimed micrometeorites burning up in the upper atmosphere, perhaps) made the atmosphere rotate a little faster, friction would slow it down again, passing some of its energy on to the Earth.

 

[russ_watters]

They once thought you would not be able to breathe if you moved faster than a horse could gallop.

Do you have a source for that? Surely nobody noticed breathing problems while riding a horse and people experienced faster winds (and horse + wind). Sounds like an old wive's tale to me.

 

[A.T.]

i didn't say they were living in supersonic wind. i asked WHY they don't.

Then I must have misunderstood. You seemed to assume the supersonic wind, and asking why there are no sonic booms:

Why doesn't the Earth crust moving under all that air produce a sonic boom, or constant sonic boom, or something?

 

[Office_Shredder]

He says why doesn't the Earth's crust move under the air, that's asking why the wind doesn't exist.Edit to add: with that said, I thought the atmosphere did move net west to east on average, because the rotation is not literally in sync with the earth. Is that true? Many of the responses here make it sound like that is false.

 

[Arjan82]

I believe that depends on the hemisphere you are on:

These are the trade winds. I'm not sure if they average out to zero however.

 

[Vanadium 50]

hese are the trade winds. I'm not sure if they average out to zero however.

If they don't, where does the air accumulate? And what part of Earth will soon be under vacuum?

 

[russ_watters]

I do not follow. in air you can move faster than the speed of sound because it's not as dense. in liquid, the speed of sound is higher and it is much denser. so moving faster than the speed of sound under water seems impossible. unless you're talking about moving in a cavitation bubble, then you're not really moving in liquid, but in air. so... i have no idea

This doesn't follow the logic of your opening post: your logic was that since the atmosphere is not firmly attached to the Earth, it should not rotate with the Earth. The same logic will take you to the same place with the oceans. But you seem to recognize the flaw regarding the oceans (drag), so...?

Also note it's not about the speed of sound itself, which is higher in water.

 

[russ_watters]

If they don't, where does the air accumulate? And what part of Earth will soon be under vacuum?

To the east.

(There is no need for them to accumulate.)

 

[russ_watters]

Also, it's believed that some of the water on Earth did in fact start off moving tens of thousands of mph, so it did need to stop somehow.

 

[jbriggs444]

If they don't, where does the air accumulate? And what part of Earth will soon be under vacuum?

The mean torque of Earth on atmosphere must be zero, else angular momentum would build without bound. That entails neither that the mean east-west surface wind velocity be zero nor that the net spinward flow rate be zero.

 

[Arjan82]

If they don't, where does the air accumulate? And what part of Earth will soon be under vacuum?

The Earth is round, so you can have an average westerly flow while avoiding a vacuum

 

[Arjan82]

Also, it's believed that some of the water on Earth did in fact start off moving tens of thousands of mph, so it did need to stop somehow.

You mean when it surged through the atmosphere on the back of a comet?

 

[Vanadium 50]

To the east.

Well, my comment was somewhat tongue-in-cheek, but the point is that the continuity condition constrains what the air can do. An average rotation is one solution. (I think the requirement is no net flow across lines of latitude). But this is kind of a digression - I think the difference between water and air is at the base of the OP's misunderstanding: if an ocean of water gets carried with the earth, why not an ocean of air?

 

[Office_Shredder]

http://adsabs.harvard.edu/full/1966SSRv...6..248KThis has some interesting things to say right on the first page. If you go up high enough you do get maybe west to east motion of about 100m/s measured by looking at satellite drift over time?, and also the upper atmosphere moving approximately with Earth is hypothesized to be at least in part driven because charged particles in the upper atmosphere get dragged along with Earth's magnetic field.

This was written in 1966, it feels like there must be something more up to date (I'm surprised they could measure satellite orbital drift back then...)

 

[hmmm27]

Earth rotates faster than the speed of sound at the equator, but it doesn't produce a sonic boom, why?

It does. Well, sortof.

Rather than the measly hundreds of meters per second that the Earth's atmosphere has as a speed-of-sound, the solar wind is trucking along at hundreds of kilometers per second. But, not many particles make it past the magnetic field to impact the atmosphere. So, you'd get a pretty lightweight "sonic hiss", maybe.

 

[ardnog]

Do you have a source for that? Surely nobody noticed breathing problems while riding a horse and people experienced faster winds (and horse + wind). Sounds like an old wive's tale to me.

I heard it in the early 1980s on a British childrens's TV education show called Eureka in which actors dressed up in period costumes and re-enacted the creation of famous inventions. So based on western technological progress and British culture I assume it stems from the industrial revolution era.

I tried to find the quote with google, and the best I could do was a misattribution to Dionysius Lardner who was misattributed as saying "Rail travel at high speed is not possible because passengers, unable to breathe, would die of asphyxia". https://en.wikiquote.org/wiki/Dionysius_Lardner

I feel that going further will involve contacting the BBC or purchasing the old TV episodes, so I've now reached the limit of the amount effort I'm prepared to put into defend the quote. :-) While it does sound like a ludicrous statement if true (and it may not be true), it wouldn't have been the dumbest thing that's ever been said by an expert.

 

[Janus]

Do you have a source for that? Surely nobody noticed breathing problems while riding a horse and people experienced faster winds (and horse + wind). Sounds like an old wive's tale to me.

When the first steam trains were introduced there was concern by some in the general populace that you wouldn't be able to breathe moving that fast, or that the vibrations would knock you unconscious. Of course these fears were unfounded, and anyone who put some thought to it, ( such as considering that, as you pointed out, people had already experienced comparable relative air speeds with no ill effects) would have quickly realized this.

 

[Klystron]

To help resolve possible confusion identified in earlier posts between the physics of air and water, atmosphere and ocean; consider using the simpler collective term fluid.

In physics, a fluid is a substance that continually deforms (flows) under an applied shear stress, or external force. Fluids are a phase of matter and include liquids, gases and plasmas. They are substances with zero shear modulus, or, in simpler terms, substances which cannot resist any shear force applied to them.

Along with helping understand underlying concepts such as shear and friction, using the term fluid includes water vapor in the atmosphere, dissolved gases in the ocean and relevant transitions such as ice, fog, steam, clouds and rain; and measures such as temperature and density that influence 'speed of sound'.

 

[anuttarasammyak]

The examples of fluids move with solid surroundings are

Newton's bucket : water in the rotating bucket also rotate with same angular speed with the bucket

Centrifugal Uranium enrichment : UF6 gas in rotating cylinder also rotates with cylinder and get centrifugal force according to isotope weight.