The section of my physics book on sound makes no sense

[Tim.thelion]

ok I am in consepual physics 7th edition by paul g hewit and the sound section makes no sense... It is really badly written ie it tells about media storage but not about sound...

ok here is my problem:
chapter 18 it says that speed of a wave = frequency * wavelength

chapter 19 it says that the speed of sound does not depend on the frequency with no further explenation other than to say that the speed of sound changes with diferences in weather.

can someone bring some sense to this?

does this mean that the wavelength of a 'c' note changes based on the condition since the frequency of a 'c' note is always the same?

 

[mezarashi]

The frequency of any wave cannot change. This is because you cannot have peaks or troughs disappearing. It can only "appear" to change once you start studying the Doppler effect.

The speed of sound does not depend on frequency. The speed of waves in anything does not depend of frequency. It depends on the 'nature' of the medium in which it is travelling. Weather will affect the condition of air. Air is the medium in which sound travels. You can make a wave travel faster in a string by making the string tighter (i.e. change in medium - the string's nature).

 

[Tim.thelion]

I gues my question is if we hear 264 hz as 'c' in all weathers does that mean that on a cold day 'c' will have a diferent wavelength than on a warm day?

 

[mezarashi]

Yes. If the velocity changes (the medium changes), the wavelength will change accordingly to accommodate (v = fh) because frequency cannot change.

 

[Tim.thelion]

so we distingush between diferent types of light by the wavelength and we distingush between diferent types of sound by the frequency... interesting

 

[Chi Meson]

so we distingush between diferent types of light by the wavelength and we distingush between diferent types of sound by the frequency... interesting

Any type of wave can be distinguished by either it's frequency or it's wavelength. Since wavelength is the result of a particular sound (f) in a particular medium(v), the wavelength is less of a distinguishing feature as compared to frequency; since the speed of sound can change so easily, it is better to use frequency for distinguishing sounds.

Light has the benefit of having a universal constant as its speed. So it is perfectly equivalent to use frequency or wavelength to distinguish a particular "color" of light. It seems to be more useful to refer to light's wavelength; I'm not exactly sure why.