Friday, March 29, 2024
03:16 PM (GMT +5)

Go Back   CSS Forums > CSS Compulsory Subjects > General Science & Ability > General Science Notes

Reply Share Thread: Submit Thread to Facebook Facebook     Submit Thread to Twitter Twitter     Submit Thread to Google+ Google+    
 
LinkBack Thread Tools Search this Thread
  #1  
Old Saturday, September 27, 2008
Faryal Shah's Avatar
Senior Member
Medal of Appreciation: Awarded to appreciate member's contribution on forum. (Academic and professional achievements do not make you eligible for this medal) - Issue reason:
 
Join Date: Apr 2007
Location: karachi & hyderabad
Posts: 522
Thanks: 153
Thanked 448 Times in 211 Posts
Faryal Shah will become famous soon enough
Default Sound Waves

Sound Waves


Sound is a series of compression waves that moves through air or other materials. These sound waves are created by the vibration of some object, like a radio loudspeaker. The waves are detected when they cause a detector to vibrate. Your eardrum vibrates from sound waves to allow you to sense them. Sound has the standard characteristics of any waveform.

Questions you may have include:
  • What is sound?
  • What are the characteristics of sound?
  • How is sound created and detected?



Sound is waveform in matter
Sound is a waveform that travels through matter. Although it is commonly associated in air, sound will readily travel through many materials such as water and steel. Some insulating materials absorb much of the sound waves, preventing the waves from penetrating the material.

Does not travel in vacuum
Because sound is the vibration of matter, it does not travel through a vacuum or in outer space. When you see movies or TV shows about battles in outer space, you should only be able to see an explosion but not hear it. The sounds are added for dramatic effect.

Some atoms in space
Note that in outer space, there are actually some widely-spaced atoms and molecules floating around. But since they are so far apart, regular wave motion would not be great enough to detect.

Sound waves different than light waves
Also note that light and radio waves are electromagnetic waves. They are completely different than sound, which is vibration of matter. Electromagnetic waves are related to electrical and magnetic fields and readily travel through space.

Sound is a compression wave
The back-and-forth vibration of an object creates the compression waves of sound. The motions of a loudspeaker cone, drumhead and guitar string are good examples of vibration that cause compression waves. This is different than the up and down or transverse motion of a water wave.







Characteristics of sound
A sound wave has characteristics just like any other type of wave, including amplitude, velocity, wavelength and frequency.

Amplitude
The amplitude of a sound wave is the same thing as its loudness. Since sound is a compression wave, its loudness or amplitude would correspond to how much the wave is compressed. It is sometimes called pressure amplitude.

Decibel
A common measurement of loudness is the decibel (dB). It is really 1/10 of a bel, which was named after the inventor of the telephone, Alexander Graham Bell. It is a complex unit that varies as the ratio of the logarithms of loudness.

Decrease in loudness
A sound wave will spread out after it leaves its source, decreasing its amplitude or loudness. The amplitude decreases as the square of the distance from the source. Also, if there is some absorption in the material, the loudness of the sound will decrease as it moves through the substance.

Speed or velocity of sound
The speed or velocity of sound in air is approximately 344 meters/second, 1130 feet/sec. or 770 miles per hour at room temperature of 20oC (70oF). The speed varies with the temperature of air, such that sound travels slower at higher altitudes or on cold days.

Note: The difference between speed and velocity is that velocity usually includes direction the of travel. We'll interchange them here, but in some cases the distinction is important.

A jet plane traveling at the speed of sound would be moving at about 680 mph at sea level. At very high altitudes, the speed required would be much lower.


Wavelength
Wavelength is the distance from one crest to another of a wave. Since sound is a compression wave, the wavelength is the distance between maximum compressions.

Frequency
The frequency of sound is the rate at which the waves pass a given point. It is also the rate at which a guitar string or a loud speaker vibrates. Frequency is also called the pitch of a sound. It is called the note in musical sounds.

Relationship
The relationship between velocity, wavelength and frequency is:

velocity = wavelength x frequency

Since the velocity of sound is approximately the same for all wavelengths, frequency is often used to better describe the effects of the different wavelengths.

Pitch
The pitch or note of a sound that we experience is determined by its wavelength or its frequency. The shorter the wavelength, the higher the frequency becomes, and the higher the pitch that we hear.

Creating and detecting sounds
Creating and detecting sounds are similar effects, but opposite. They demonstrate the duality of nature.

Creating sound
Whenever an object in air vibrates, it causes compression waves in the air. These waves move away from the object as sound. There are many forms of the vibration, some not so obvious.

The back and forth movement of a loudspeaker cone, guitar string or drum head result in compression waves of sound. When you speak, your vocal cords also vibrate, creating sound.

Blowing across a bottle top can also create sound. In this case, the air inside the bottle goes in a circular motion, resulting in sound waves being formed. Wind blowing through trees can also create sound this indirect way.

Sound can also be created by vibrating an object in a liquid such as water or in a solid such as iron. A train rolling on a steel railroad track will create a sound wave that travels through the tracks. They will then vibrate, creating sound in air that you can hear, while the train may be a great distance away.

Detecting sound
When a sound wave strikes an object, it can cause the object to vibrate. This leads to the method to detect sound, which requires changing that vibration into some other type of signal--usually electrical.

The main way you detect or sense sounds is through your ears. The sound waves vibrate your ear drum, which goes to the inner ear and is changed to nerve signals you can sense.

You can also feel sounds. Stand in front of a stereo or hi-fi loudspeaker on at full volume, and you can feel some of the vibrations from the music.

There are mechanical devices that detect sounds, such as the microphone. The sound vibrates a membrane, which creates an electric signal that is amplified and recorded.


Summary
Sound is a compression waveform created by the vibration of some object. Sound moves through air or other materials. The characteristics of sound are that it has amplitude, wavelength, frequency and velocity. Sound must cause another object to vibrate to be detected.




regards

faryal shah
__________________
Go confidently in the direction of your dreams. Live the life you have imagined.
Reply With Quote
The Following 5 Users Say Thank You to Faryal Shah For This Useful Post:
aasho (Thursday, November 20, 2008), ASP imran khan (Monday, August 16, 2010), iamcalledasad (Thursday, April 02, 2009), Na_shah (Thursday, April 16, 2009), Sureshlasi (Wednesday, October 01, 2008)
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
EDS- notes Predator General Science Notes 70 Sunday, February 28, 2016 12:05 PM
GK paper 1(EveryDay Science) Argus CSS 2005 Papers 25 Tuesday, December 03, 2013 03:22 AM
Solved Everyday Science Papers Dilrauf General Science & Ability 4 Friday, April 08, 2011 06:10 PM
How things work? dr.janxeb General Science Notes 24 Wednesday, September 09, 2009 11:07 PM
Ocean waves and tides Naseer Ahmed Chandio General Science Notes 0 Thursday, December 14, 2006 02:13 PM


CSS Forum on Facebook Follow CSS Forum on Twitter

Disclaimer: All messages made available as part of this discussion group (including any bulletin boards and chat rooms) and any opinions, advice, statements or other information contained in any messages posted or transmitted by any third party are the responsibility of the author of that message and not of CSSForum.com.pk (unless CSSForum.com.pk is specifically identified as the author of the message). The fact that a particular message is posted on or transmitted using this web site does not mean that CSSForum has endorsed that message in any way or verified the accuracy, completeness or usefulness of any message. We encourage visitors to the forum to report any objectionable message in site feedback. This forum is not monitored 24/7.

Sponsors: ArgusVision   vBulletin, Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.