Sound!!!

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# Sound!!! - PowerPoint PPT Presentation

Sound!!!. Sound is a  longitudinal  wave. Longitudinal waves are made up of areas where the wave is compressed together, and other areas where it is expanded. Think about it: How do we make sound? How do we hear sound?.

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## PowerPoint Slideshow about ' Sound!!!' - mulan

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Presentation Transcript

### Sound!!!

Sound is a longitudinal wave
• Longitudinal waves are made up of areas where the wave is compressed together, and other areas where it is expanded.
• Think about it: How do we make sound?
• How do we hear sound?
Let’s look in detail at three fundamental characteristics of sound: speed, frequency, and loudness.
Speed
• The speed of sound in air actually depends on the temperature of the air. Why do you think this is?

v = 331.5m/s + 0.6T

Did you know?
• On October 15, 1997 the British built "Thrust SSC" vehicle became the first land based vehicle to break the sound barrier. To be official it had to break the sound barrier twice within one hour. It did this, with an average top speed on the two runs of Mach 1.020. The runs took place in early in the day so that the temperature of the air (and the speed of sound) would be lower. As an interesting side note, this record was set one day after the 50th anniversary of the first supersonic flight made by Chuck Yeager on October 14, 1947 in the "Bell X-1."

v = 331.5m/s + 0.6(-5)

v = 331.5m/s + -3m/s

v = 328.5 m/s

Assumption
• At 15oC, sound travels at a speed of 340 m/s. Unless otherwise specified, use this value.
Lightning
• If lightning flashes and makes a sound at the same time, why do you see it first and hear the thunder so much later?
Sound in different media
• In which medium will sound travel faster?
Frequency
• The number of waves that pass a given point per unit of time.
• Unit: cycles per second = Hz
Frequency
• What sort of frequencies of sound will you typically be talking about?
• Most often we will be looking at sound waves that humans can actually hear, which are frequencies from 20 – 20 000 Hz.
• Check out the specifications for headphones printed on the back of the package. They’ll probably list their range from 20 – 20 000Hz, since that’s what the average person can hear.
• 20 Hz would be very deep, low, rumbling sounds.
• 20 000 Hz would be a very high pitched, squealing sort of noise. (In music “pitch” means the same as frequency.)

Example 2: My wife and I are listening to my favorite David Bowie song, “Major Tom” from the 1980’s. At one point the singer hits a note that my wife thinks has a wavelength of 0.014m. I tell her this is impossible… explain why.

I play the trumbone (yes, I actually can, I’m just not very good anymore!), and tuned it straight out of the case. The temperature of the trombone was 17°C and I tuned it to  13,000 Hz. I start playing the trombone, and by the time I’m a few minutes into the song I notice that the notes all seem wrong. If the trombone has warmed up to my body temperature (37°C) , determine what my original tuned note has changed to. (Note: the wavelength of the wave will not change with a change in temperature.)

Loudness
• The loudness of a sound depends on the wave’s amplitude.
• This is why a stereo system has an “amplifier”, a device that increases theamplitude of sound waves.
• The louder a sound, the bigger the amplitude.
• This is also a way of measuring the amount of energy the wave has.
Loudness
• The system used to measure the loudness of sounds is the decibel system, given the unit dB.
• The decibel scale is a logarithmic scale. A sound is 10 times louder for each 10 decibel increase. (Or, loudness doubles for each increase of 3 decibels.)

Most concerts you go to will have sound levels between 100 – 130 dB… easily into the permanent damage range.

Did you know?!
• One of the loudest man-made sounds is created by the space shuttle lifting off. It will generate sounds at an incredible 215 dB!!! The sound is so loud that it would actually cause damage to the launch tower, and as a reflected echo, to the shuttle itself. To absorb the energy, huge amounts of water are pumped to the base of the launch pad seconds before takeoff. The water absorbs the sound, as well as a lot of heat. When you see video of a shuttle launch, most of the white stuff you see billowing from the launch pad right at takeoff is not smoke... it\'s steam!