Falcon Heavy Launch

Lawman

Well-Known Member
So sound actually refracts upwards in our atmosphere, in general. A jet at altitude for example. The colder the air the slower the speed of sound, and with a normal lapse rate, the air gets warmer as you go down, where the speed of sound is faster. The sound waves that initially propagate downwards are moving from a slower medium to a faster medium. This will refract up. If you took a cross section of it, especially at and angle, the bottom of the wave would hit the faster medium first, speeding up first and the top of the wave last. This also stretches the wave and increases the wavelength. Which makes sense because wave velocity = frequency * wavelength. If the velocity is increasing, and frequency is set by the source(a constant in our example), the length must also increase.
I tried to make a simple drawing real quick to hopefully better illustrate my point. Also note, that at some point on the ground there will be a shadow where you cannot hear the sound due to refraction, even though you may be able to see the source.
Black Magic & Sorcery ... got it.



Ive actually had a similar problem explaining to others why artillery shells and rockets moving over the battlefield don’t have the inherent sonic boom people expect between their launch and impact points. People expect a sonic boom to be a single loud noise, they don’t realize the “runaway freight train” sound as the round passes overhead is actually a continuous series of booms created as the round/rocket changes both velocity and relative temp with altitude. It’s even more prevalent with high angle fire vs flatter trajectory.
 
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z987k

Well-Known Member
Black Magic & Sorcery ... got it.



Ive actually had a similar problem explaining to others why artillery shells and rockets moving over the battlefield don’t have the inherent sonic boom people expect between their launch and impact points. People expect a sonic boom to be a single loud noise, they don’t realize the “runaway freight train” sound as the round passes overhead is actually a continuous series of booms created as the round/rocket changes both velocity and relative temp with altitude. It’s even more prevalent with high angle fire vs flatter trajectory.
You also have the Doppler effect, which is the high to low pitch change when trains, or really anything, passes.
That would actually make a super cool video. A missile or even artillery round passing overhead and it's sound. Along with a radiosonde's atmospheric data for nearby. You could, with math, predict where the sound would be heard(and not heard) and the change in sound a human would perceive in a given location relative to time. And then show that math happening in the video.
That's the kind of thing, at least in my mind, you can show to the high school math student that asks why or when will I use this. And it's not hard math. Anyone that understands trig can do this.
And the idea could be put to quite the benefit, you could reasonably figure out how to take a shot at a target and given the right conditions have someone just 100 yards away not hear a thing.
On that note - this is a pretty cool book. The author talks about how some civil war battles were likely significantly effected by sound wave refraction and acoustic shadows. https://www.amazon.com/Civil-Acoust...56&sr=8-1&keywords=civil+war+acoustic+shadows
 

z987k

Well-Known Member
No I get that it happens at altitude. Here is my 7th grade geometry attempt. Z is where the sonic transition happens. X is the landing spot and Y is the spectators.
View attachment 41901
After the transition happens the lander is still falling very fast if not right below the speed of sound so the actual boom sound isn't to much faster than it is falling up until almost a 1000 feet above the pad when they do the landing burn and slow way down. Those thing where moving! Since the crowd was farther away than being right under the transition is took longer for the boom to reach them then if they were standing on the pad. So that extra distance the sound had to travel to reach the spectators gave the landers (visually) time to almost be on the pad when they hear the booms.
Fingers and head hurt.
Yep, I think you are right. But I think the transition is much higher than 1000 feet. And they are actual slowing down to Mach 1 not speeding up.

The second part of the equation I think (as @z987k pointed out) is the direction the sound wave is traveling is generally downward so it likely hits the ground first and then expands outward.

It's been 30 years since I studied this stuff.....brain hurts just trying to think about it.
I completely missed fast89poney's post and that you were replying to him.

The reason the rockets are on the ground before you hear the sonic booms is because of the difference in the speed of sound and the speed of light. Not the difference in straight line distance between the landing pad and the observer. The further the distance, the greater the sound delay.
I did the math, as I am apt to do. Because science without math is called fiction. Anyways, from the distance of the VAB to the pad the boosters landed on, you'd expect around a 46 second delay between seeing it and hearing it. And about a 16 second delay on the main launch since it was closer.
 
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av8tr1

"Never tell me the odds!"
I completely missed fast89poney's post and that you were replying to him.

The reason the rockets are on the ground before you hear the sonic booms is because of the difference in the speed of sound and the speed of light. Not the difference in straight line distance between the landing pad and the observer. The further the distance, the greater the sound delay.
I did the math, as I am apt to do. Because science without math is called fiction. Anyways, from the distance of the VAB to the pad the boosters landed on, you'd expect around a 46 second delay between seeing it and hearing it. And about a 16 second delay on the main launch since it was closer.
No worries. You're explanation was SOOOOOO much better than mine. "You are smart. you will make us strong."
 

U_of_I_Tweak

Well-Known Member
No worries. You're explanation was SOOOOOO much better than mine. "You are smart. you will make us strong."
Good grief.....did I just make a Star Trek quote????? I gotta get more sleep.....
I read the first post and thought to myself, there's no way that was an obscure TNG quote...

Then I read your follow up. I don't know if anyone else recognized it, but I appreciated it!

"We are strong!"

Sent from my Pixel 2 XL using Tapatalk
 

killbilly

Vocals, Lyrics, Triangle, Washboard, Kittens
I read the first post and thought to myself, there's no way that was an obscure TNG quote...

Then I read your follow up. I don't know if anyone else recognized it, but I appreciated it!

"We are strong!"

Sent from my Pixel 2 XL using Tapatalk
God help me, but I recognized it, too.

If only because that was one of the more shark-jumpy episodes they've done.....
 

Cptnchia

Dissatisfied Customer
Good grief.....did I just make a Star Trek quote????? I gotta get more sleep.....
I read the first post and thought to myself, there's no way that was an obscure TNG quote...

Then I read your follow up. I don't know if anyone else recognized it, but I appreciated it!

"We are strong!"

Sent from my Pixel 2 XL using Tapatalk
God help me, but I recognized it, too.

If only because that was one of the more shark-jumpy episodes they've done.....
@U_of_I_Tweak @killbilly

As a soldier of the force in the Star Wars Vers Star Trek conflict, I’m so ashamed.
Y’all being racist about Pakleds!



They’re just looking for things that make them go. What’s so wrong with that?


:)
 
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