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All right, welcome to the NASA Connect studio.

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Now joining me in the studio are Rich Silcox, a senior research scientist, and we're also

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now joined by Dennis Huff from NASA Glenn Research Center in Cleveland, Ohio.

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But before we talk to our researchers, let's give you a chance to do some analyzing using

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the data from the experiment you just saw.

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After this segment, our two researchers will be answering your email questions and taking

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questions from the viewing audience.

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Okay now, look carefully at the data and using the information in the following diagram,

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work with your fellow students to answer the questions as read aloud by Rich Silcox.

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As the distance increased from 50 meters, what happened to the mean time?

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Use the formula, percent of experimental error, equals calculated value minus the

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accepted value, divided by the accepted value, times 100, to calculate the percentage of

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error at 50 meters and 300 meters.

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Why do you think they are different?

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The speed of sound is directly proportional to air temperature.

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Is the speed of sound faster in the summer or winter?

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Why?

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All right, we're back, and with me are Rich Silcox and Dennis Huff to answer your questions.

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But let's start things off by asking Dennis, what is it, Dennis, that you actually do there

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at NASA Glenn?

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I'd be glad to answer that.

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Hello, my name is Dennis Huff, I'm the chief of the acoustics branch at NASA's Glenn Research

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Center that's located in Cleveland, Ohio.

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Our contribution to quieting the skies looks at ways to making the engines quieter.

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Our goal is to develop engine noise reduction technology without compromising the engine

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performance or the aircraft's safety.

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Some members of our team develop mathematical models to be able to predict the sound from

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the engine, while others test different parts of the engine inside wind tunnels and anechoic

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chambers.

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Our best noise reduction concepts will eventually be tested on engines to make sure we can really

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make the airplanes quieter.

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You've got a lot of good stuff going there that I could ask a lot of questions about,

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and I just might do that, Dennis, but I've got some e-mail questions that have come in

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for both you guys.

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So let me start with an e-mail question.

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The first question is, does the shape of a plane affect the sound?

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And this is from Jonathan in Virginia Beach.

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Yeah, Shelley, the shape of the airplane does change the sound dramatically.

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For instance, when the airplane is coming in for a landing or taking off, the flaps

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in the landing gear are deployed.

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In that case, the flow is very dirty and it makes a lot more noise than when those components

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are stowed away.

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Yes, and in fact, it's interesting on the engine itself.

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You'll notice that some of the older aircraft have smaller diameter engines, and the smaller

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diameter actually passes a lot more flow at a higher velocity, and this causes the jet

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noise to be very loud.

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We have a general rule of thumb that we say that the velocity of the exit of the velocity

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raised to the eighth power is proportional to the jet noise.

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So the newer aircraft that have larger diameter engines actually end up being quieter.

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All right.

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Let's go back.

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You've probably kind of answered this already, but I'm thinking about me who flies an awful

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lot on these small little, they call them puddle jumpers, or commuter planes compared

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to your bigger 757s.

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How is there a difference on those size of engines and the noise that they are generating?

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Sure.

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Those engines are some of the newer engines.

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We call those higher bypass ratio engines, and so you've got a lot of flow going through

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that.

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It's a lot of thrust in that engine, but it's going at a lower velocity, so it's a much

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quieter engine than the older ones.

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Oh, okay.

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In a lot of cases, the propeller airplanes are quieter, too.

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They're quieter than the large jets are.

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All right.

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I've got a question.

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You keep talking about research to reduce noise around communities.

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What is the community that you all are referring to here?

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Well, generally we're talking about that area around the airport that's affected by the

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operations of the airplanes taking off and landing.

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Once the airplane climbs to altitude and is at cruise altitude, maybe at 35,000 feet,

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you don't really hear it much anymore.

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Okay.

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All right.

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Good.

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Well, I've got someone telling me we've got a caller out there, so let's go ahead and

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take that caller.

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Caller, could I have your first name, please, and your question?

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My name is Timothy, and my question is, how fast is the sound of sound travels through

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water?

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Oh, okay.

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The sound traveling through water.

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And is there a difference between the speed that sound travels in air and water?

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Yes.

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The speed travels through water much more quickly than it does in air.

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I can't recall the exact number.

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I think it's three or four times faster in water than it is in air.

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Okay.

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All right.

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So we know that it is going to travel faster through water than in air.

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Good question there, Timothy.

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I'm going to take a final question I have here by email very quickly.

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Well, no, final advice.

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What advice would you, Dennis, give to viewers about thinking about careers?

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I'd be glad to answer that.

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My father gave me the advice to keep your options open.

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You can get into a lot of different activities and make sure you involve yourself in extracurricular

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activities, but also stay with your math and science and your English.

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All the different courses are very important.

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All right.

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There, you've heard it from us.

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And I see we're quickly running out of time.

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Thank you, Dennis and Rich.

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And now, students from Jonas Clark Middle School in Lexington, Massachusetts, share

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some technology notes that are sure to sharpen your investigation on sound following this

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program.

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One part of the website is called the NASA Sound Machine.

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With it, you'll learn about the shapes and characteristics of sand waves, how an

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airplane produces different kinds of noise, and what certain words would sound like if

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you had severe or partial hearing loss.

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Another part of the NASA Connect website features NASA researchers talking about their jobs.

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It's called Career Corner.

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There's also a fun quiz that will test your knowledge of sound and hearing.