CONCEPT: Pitch versus volume

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• UNSW - Pitch & Frequency

CONCEPT: Sound - Pitch versus volume

• Does hitting an object harder make its sound louder, softer or no different?
• Does hitting an object harder change the type of sound it makes (pitch)?

In most cases, hitting an object lightly or heavily has no affect on the frequency (pitch) of the sound that is produced.

Many elementary textbooks say that sound travels 'better' through solids and liquids than through air/gases, but they are incorrect: air, solids, and liquids are nearly transparent to sound waves.

It's true that the speed of sound differs in each material, but this does not affect how well they conduct. “Faster” doesn't mean “better.”

It is true that their transparency is not exactly the same, but this only is important when sound travels a relatively great distance through each material.

This may sound confusing: The trick is to remember that with sound, as with life, 'faster' does not equal 'better'

Sound waves are introduced into a medium by the vibration of an object - say a guitar string.

The amount of energy that is transferred to the medium is dependent upon the amplitude of vibrations of the string. If more energy is put into the plucking of the string (that is, more work is done to displace the string a greater amount from its rest position), then the string vibrates with a greater amplitude. The greater amplitude of vibration of the guitar string thus imparts more energy to the medium, causing air particles to be displaced a greater distance from their rest position. Subsequently, the amplitude of vibration of the particles of the medium is increased, corresponding to an increased amount of energy being carried by the particles.

The amount of energy that is transported past a given area of the medium per unit of time is known as the intensity of the sound wave. The greater the amplitude of vibrations of the particles of the medium, the greater the rate at which energy is transported through it, and the more intense that the sound wave is.

Typical units for expressing the intensity of a sound wave are Watts/meter2

Reference: http://www.physicsclassroom.com/class/sound/Lesson-2/Intensity-and-the-Decibel-Scale

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How sound travels - When sound waves in the air hit a solid object (like a brick wall), the sound waves are mostly reflected

Sound is reflected usually reflected when it meets a barrier between different types of media (say when travelling through air and hitting a solid). The laws of reflection are the same for all types of waves, including light and sound.

http://www.acoustics.salford.ac.uk/feschools/waves/reflect.php

When a wave reaches the boundary between one medium another medium, a portion of the wave undergoes reflection and a portion of the wave undergoes transmission across the boundary.

The amount of reflection is dependent upon the dissimilarity of the two media.

A hard material such as concrete is as dissimilar as can be to the air through which the sound moves; subsequently, most of the sound wave is reflected by the walls and little is absorbed.

Reflection of sound waves off of surfaces can lead to one of two phenomena - an echo or a reverberation. A reverberation often occurs in a small room with height, width, and length dimensions of approximately 17 meters or less. Why the magical 17 meters? The effect of a particular sound wave upon the brain endures for more than a tiny fraction of a second; the human brain keeps a sound in memory for up to 0.1 seconds. If a reflected sound wave reaches the ear within 0.1 seconds of the initial sound, then it seems to the person that the sound is prolonged.

Reference: http://www.physicsclassroom.com/class/sound/Lesson-3/Reflection,-Refraction,-and-Diffraction