/sci/ - Science & Math

[Anonymous No.5775512]

Hey /sci/, it's /tg/ here.

We got into a discussion about planets with supersonic winds. I've heard that Jupiter and Venus have what's referred to as "wind that exceeds the local speed of sound."

Can you guys explain what that means?

Everyone likes to understand things in terms that are familiar to them, so can someone explain what would happen if you tried to communicate via sound on one of these planets?

Let's assume we're superhumans and can withstand the environment. We stand some distance away from one another and yell really loudly into a super-duper megaphone that is really, really fucking loud.

"FUCK YOU!" I say to my friend.

Assuming we're standing in supersonic winds, what happens? Does the sound get carried along with the supersonic winds, essentially creating a new sound barrier? Is it for some reason slowed down by the winds? Let's assume that the wind is blowing away from Anon1 and towards Anon2. Both Anons yell "FUCK YOU!" What does each Anon hear?

[Anonymous No.5775522]

Here's the thread, for reference. Come laugh at us and our feeble attempts at scientific thought.

>>>/tg/24955762

[Anonymous No.5775548]

>>5775522
I like how a guy brings up the Wright Brothers and it gets derailed to talking about WWII.

[Anonymous No.5775563]

>>5775548
And moon nazis, don't forget the moon nazis.

[Anonymous No.5775581]

The speed of sound is a thermodynamic property I believe. Then we define the Mach number as the quotient between the speed of the fluid, and the speed of sound, when M is greater than 1 we have supersonic speed, since the speed of sound is the speed at which a small perturbation travels, if you go faster than that, the air ahead of you doesnt receive the information of 'okay there is something coming to us, lets adapt to it', and so you can have discontinuities called 'shock waves'

[Anonymous No.5775583]

Say you have a big jumble of gas particles. Normally if you push on some gas particles, those gas particles will push on other gas particles, and the time that it takes between one gas particle hitting the next one will depend on how densely the particles are packed and how fast they're all moving. The speed of sound is really just an expression for how quickly a wave of movement spreads through the medium.

For an analogy, imagine a big bowl of jello or a block made out of smaller blocks with springs connecting them to other blocks in each direction. If you poke one edge of the spring block or one edge of the jello, you can see a wave of movement that propagates from the edge you poked to the other side.

That's what "local speed of sound" is - it's an expression of how quickly a wave of pressure or movement can spread through the air given local conditions.

So, if you have supersonic wind, what that means is that you have a slug of air which is moving faster than that speed. To return to the jello example, it would be like using a railgun to shoot a slug of jello through a stationary brick of jello a meter across versus, say, gently smooshing the jello slug into the surface of the brick.

Nothing about the speed of sound has changed here, because sound depends on bouncing air to propagate. If you're inside the wave of supersonic air, if you can hear at all, you'll perceive sound as propagating at the normal rate - it's just that both you and local particles
cont

[Anonymous No.5775588]

>>5775512
One hears it and one dosent
Think of it as a straight line
A --- fuck you ---- B ---- fuck you
Only person B hears it since no one is their to yell it to person A

[Anonymous No.5775595]

>>5775583
are all moving faster relative to the ground than sound waves normally do.

If one person is outside the packet of supersonic wind and the source is inside, then I think they'll perceive the sound as being doppler shifted up or down depending on which direction the wind is traveling. But they won't hear the sound until way after the thing has gone by.

[Anonymous No.5775635]

If anon A is upwind yelling at anon B, The sound will travel at the local speed of sound relative to the medium, which is the wind moving damn fast. So the sound will travel at the local speed of sound + the speed of the wind. The sound will reach anon B faster and lower in pitch (the sound effectively has a longer wavelength now). If anon B tried screaming over to A and the winds were supersonic going from A to B, then the sound wouldn't reach A (unless it went around the world or some such shit). Also the sounds would form shockwaves like in part 3 of this picture.

[Anonymous No.5775640]

>>5775635
whoops, first sentance should say "If anon A is yelling downwind at anon B,..."

[Anonymous No.5775642]

>>5775635
>>5775583
>>5775581

Thanks for the answers, guys. This is really interesting stuff.