Sonic Boom?

When an object aircreaft goes at above the speed of sound a pressure wave builds up, this then breaks away and causes the sonic boom.

Check out this link for a nice explanation: http://en.wikipedia.org/wiki/Sonic_boom.

Psst: a number of questions you've posted lately can be answered well and completely (more so than we can do here, generally) by following the links from a Google search. For example, the above link took about 15 seconds to locate, total. Sonic booms are hardly an esoteric subject which needs explaining by specialists. Not by any means! Much has been written on this subject, and much is available on the Internet - as a simple Google search will tell you.

I don't mean to sound harsh, but if I can google "sonic boom," so can you. Please reserve this forum's energies for the hard questions, won't you?

-e

As an engineer that recently found this page and was going to add it to "favorites", a response like this has changed my mind. "Hard" questions are a matter of point of view. Perhaps the individual was trying to find out if there were some "esoteric" influences'. Since you feel qualified to answer in the matter that you did please explain how an airplane flies inverted if the NACA foil shape creates lift on the top side of the wing due to path length or how a butter fly, flies with out camber in its wings?

If I could google for the answer and get it in less time than it took me to write this post, I wouldn't be asking it here.

-e

Simple. It's angle of attack.

The airfoil's lift is really very small and not important in the equation, but the angle of the attack on the wing is.

I assumed you knew that already.

I agree with europium on his post. He is not trying to be cruel, but practical. Imagine how annoying it would be for you if you spent all your time answering questions from colleagues at work that are already at their fingertips? It's good practice for any engineer or any person to at least make the effort to research the subject first. Then ask questions that they don't understand. Doing that may actually lead to deeper questions. The sonic boom question was very broad and non-specific. A simple search would help refine the next question (if one existed) to something meaningful and academic.

As for changing your mind based on europium's response, I think you are rushing to judgment without enough facts. I am sure you know the value of fact-based decisions in your field and I would encourage you to rethink your "findings".

I am going to assume that you a knowledgeable professional that can make a valuable contribution here and your proposed solution, in my opinion, is a lose-lose situation for all of us. If I am wrong, than perhaps you have serendipitously made the right choice.

My point exactly.

I don't mind trying to answer a question when I know the poster has made at least an initial stab at it on his own resources and, having come up with nothing, posts his question here. If I can answer his question, and if it's clear he at least tried to come up with an answer himself but couldn't - regardless of the simplicity of the question - I'm more than happy to explore it with him. But if it is clear the poster hasn't invested even a minimal amount of legwork in answering his own question, why then should I do his legwork for him? If his getting his answer is not worth an investment of his own time, why then should it be worth an investment of mine?

-e

I understand the tone of the post. I feel however that you don't hand a math book to an infant when he or she wants to learn to count so they can perform some "leg work". I had thought that this was a forum for learning and teaching. I have found out that the best way to learn a subject was to teach it, and in order to teach that subject I must nurture the student. Part of nurturing is having the patience to deal with might seem to be a small spark in hopes that one day it will become a blazing inferno.

Where do you draw the line?

-e

Don't give up not everyone here thinks they are the self appointed "Forum Cops" as apparently Europium does. STAY ON BOARD, most posts are at the very least "Interesting".

A good link. Explains why I heard a double sonic boom when the space shuttle flew overhead, although not why I only heard a single when the SR-71 flew overhead. Maybe because the SR-71 was higher when I heard that boom than the shuttle was the times I heard that boom -- so maybe the twin booms joined. Of course, the tail end of the space shuttle is a lot less sleek than the SR-71 and would probably make a louder noise.

I always heard it was exploding gremlins. You can google it.

That's actually a common misconception. The gremlins do not "explode" persay but emit a very very loud bellow before disappearing back into the alternate gremlin universe, which is where they go when you look for them.

Yeah, it was early in the morning and I misspoke.

I meant to say "angels".

(It's well known that every time the sound barrier is broken, an angel dies.)

This reminds me, there is a real need for an invention that is like those shock collars the Simpsons wore when the shrink wanted them to learn to co-operate.

Such collars could be fitted to people who pose questions and a summing network would integrate our responses and apply them at 3 AM, questioners local time.

It would also work on lazy co-workers.... :)

You don't shock lazy co-workers, you nurture them. Didn't you know?

(Btw, ever changed a diaper on a 35-year-old "infant?")

-Self-Appointed Forum Cop

shock = better compliance rate

Oh, but I've been roundly chastised! Haven't you heard?

My crime? I'm guilty of not nurturing every Tom, Dick, and Harry who comes along asking everyone for the time because he won't bother checking his own watch first. And how dare I even suggest TD&H take any initiative whatsoever! How dare I suggest such a thing, lest my prodding snuff out his creative spark?!

I'm almost tempted to dump this forum and write a book...

Candy-Ass Nation

-e

PS: And please, gimme a case of those collars, won't you?

As they say: "Catbert rules"

My apologies to Nikolai, and to the others here who were gracious enough to point out my obvious arrogance. I'm sorry.

Interestingly, my first post to CR4 decried the very kind of arrogance I posted yesterday and today. It seems I've gotten a little big for my pants lately - not to mention the fact that I also spend too much time on this forum - it is rather addictive! Consequently, this will be my last post to CR4.

Some real nice people here. Take care.

-e

well, I just use a multi tabbed browser. I hit all the e-mails and raise 20 tabs, look at the first one raised and while I wait the others load and so I can deal with them all in 10 minutes/day and I just dash them off, not grammar/typo correction....wastes time, but you knew that :)

So in the AM I look and late in the day. no more than 10 minutes each time.

so stick around.

www.maxthon.com is what I use. With thr right settking you right click and open in a new window all the stuff you like, as in new scientist etc until you have clicked 50 items. By then the first ones have loaded and so you waste almost no time.

Your inability to waste time on this site appalls me.

Why Quit --- You Do Offer Very Much To The Forum -- Maybe a little tolerance instead of quitting.

i have to say that i agree with europium, ive posted out of lazyness, and i should had investigated the matter first. But, sadly, my "idiot" posts have tons of responces when the one question i`ve posted that has a backround of study by me and that is quite especific had no response, lets say no real response.

In case you wanna help me, im insterested in finding a way to calculate sound speed in porous materials such as fiberglass in order to know the variation of the resonance frecuency of a resonator (helmholtz) when you introduce an absorbent material in the cavity (such as fiber glass). I have an idea to how to mesure it, but i want to calculate it (the sound speed in a porous material i say). I think some of the main factors are the elasticity of the fibre estructure, the fibre geometry and the density.

are you Nikolai, sir Guest?

i read the helmholtz resonator thread (started by Nikolai) and i think someone posted something on that thread about Biot's model for sound propagation thru porous materials. have you checked this out? somehow I think the answer to your question may not be simple, if that's the kind of solution you want. think about all the different kinds of porous materials there are; materials with all shapes and sizes of pores and different shapes and sizes of the stuff between them. that's got to affect the movement of sound thru the material. depending on how dense the stuff is between the pores, a general formula may need to consider that as well, and you may actually find that part of the sound arrives earlier than the rest of it because it's propagating thru two different kinds of material: the air in the pores, and the solid material between the pores. if i were you, i'd check out Biot's model. if you don't understand some of it, i'd suggest that you create a new thread and ask specific questions about the parts of the model you don't understand. there's bound to be someone here who knows something about it. if you can't get a satisfactory answer, you may wish to use an empty helmholtz resonator that you can open and put your test material inside, then see how it changes the resonance frequency. then take that figure and back-propagate it through the helmholtz equation after re-writing it with the speed of sound as the dependent variable. does this help?

thanks, im gonna check biot`s theory.

nikolai

What causes the boom

IT THE BIG DOOR AT THE WHITE HOUSE AS BUSH LEAVE'S
ACK !