Some more details on Sound

Some more details on Sound - Some more details on Sound...

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Some more details on Sound There are two main ingredients to wave motion – inertia and restoring force. These are the two ingredients that go into the mathematical description of sound waves. There are three ideas that come into play, and each idea has an equation that makes the idea very precise. To do this we will consider a sound of a definite frequency f=1/T and wavelength λ . All sound can be thought of as an addition of pure tones with definite wavelength and frequency, so this allows us to understand all sounds. First ingredient: Inertia First Idea (Newtons 2 nd Law) Because of inertia (measured in units of mass) it requires a force to change the state of motion (the velocity) of a piece of material. First Equation : F=ma (The necessary Force is equal to the mass multiplied by the rate of change of the velocity). For sound we need to think of the force per unit volume (the pressure change divided by the distance over which it changes) the mass per unit volume (the mass density) and the average velocity of air molecules. 0 mn v p T λ = p is the pressure change caused by the sound wave. λ is the wavelength – the distance over which the pressure changes. m is the average mass of an air molecule. n 0 is the normal density of molecules per cubic meter.

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• Spring '08
• SKIFF
• Fundamental physics concepts, 12 W, 10 W

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