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Speed of sound
As sound is a mechanical wave, it needs a medium to travel through, and the speed of sound is therefore dependant on the medium. The speed of sound is around 330m/s, this however, can change. This change corresponds with the medium sound is travelling through. It changes because sound travels faster and further through solids than in liquids or gases. This is because the particle theory states that particles are packed more tightly together in a solid, making it easier for the sound to travel. Sound travels slowest through gases, again due to the particle theory, which states
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that particles in a gas aren't packed together, and move freely, this makes it harder for the sound to move between the particles in a gas. The speed of sound is also dependant on the temperature of the medium, the hotter the medium, the faster the sound moves. This is because, according the particle theory, particles move faster when heated, and therefore, carry the sound faster and further. The speed of sound can be broken is very special circumstances. If a fighter jet or whip can pass the sound barrier of 330m/s, a sonic boom occurs. A sonic boom occurs when air is displaced by the object, this air has to escape quickly, and is seen as a sonic boom. A object moving faster than the speed of sound is said to be moving at supersonic speed.



























Vibration and pitch
Vibration occurs when particles move from the equilibrium position. The particles bump and bash into other through the movement of the sound waves. This movement is called vibration. Sound waves can only move with vibration, this is why when particles are more dense, such as those in a solid, sound moves faster and further, because there are more particles to move around. This is also why heat affects sound, because a heated medium will have particles that move faster, thus allowing the sound to travel faster because of increased vibration.
Pitch is caused by the differences in wavelength. When wavelengths are short, the pitch is high and the frequency will also become higher, whereas when the wavelength is long, the pitch and frequency will become shorter. High pitched waves create high sounds, and low pitched waves create low sounds. This is why all instruments sound different, as they all have different wavelengths and frequencies, even when playing the same note.

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Many Different Instruments, Many different pitches

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Echoes
An echo is when a sound is heard again, shortly after it is emitted. The sound is reflected off of a flat surface, and bounced back, the resulting sound heard as an echo. In an empty room, yelling will bring upon an echo as the walls of the room are flat, and reflect sounds easily. Yelling down a cliff, canyon or large hole will also result in an echo, as the sound waves will bounce of any flat surfaces. Movie theatres and performing arts centres have insulated walls to avoid echoes.
Doppler Effect
A motor bike is heard at a very high pitch as it approaches something, but as it passes, the sound is at a lower pitch. Why? This is because of the doppler effect. The doppler effect occurs as the motor bike in the above example pushes the sound waves in front of it closer together, and the closer together the sound waves, the higher the pitch. As the motor bike passes, the sound waves behind it aren't pushed together, and therefore, the sound is slower.










Resonance

Resonance occurs when an object vibrates in sync with the frequency of another. When this happens, the amplitude of the waves are increased, and the sound of the wave is subsequently increased. An example of this is cicadas, that massive high pitched sound that can be sometimes heard in the bush is 100's of cicadas making their sound in tune!



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To see how some of this relates to real life, go to Real World Example Video!!!!!!!
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