Physics in the Arts Lecture S5 Sound Waves Pipes I Search For The New Land Lee Morgan Musical Notes from Pressure Waves in Pipes standing waves wikipedia Sound Propagation in Air Sound reaches our ears via pressure waves traveling through air of Physics in the Arts Iowa PBS Discuss with your neighbor what are important di erences between light waves and sound waves Sound Waves Longitudinal Wave Oscillations in direction of wave velocity Sound Waves are pressure waves Iowa PBS This work by Dan Russell is licensed under a Creative Commons Attribution NonCommercial NoDerivatives 4 0 International License Based on a work at http www acs psu edu drussell demos html Sound Waves Longitudinal Wave Oscillations in direction of wave velocity Sound Waves are pressure waves Iowa PBS This work by Dan Russell is licensed under a Creative Commons Attribution NonCommercial NoDerivatives 4 0 International License Based on a work at http www acs psu edu drussell demos html Sound Waves pressure variation above 1 part in 100 000 is dangerously loud One part in 10 billion is still barely audible High pressure atmospheric pressure Low pressure e r u s s e r p distance cm x mean seal level atmospheric pressure 1 013 hPa 101 300 Pa Speed of Sound Wave Just as for transverse waves on a string v f wave speed in units m s wave length in units m frequency in units Hz 1 s In given material wave speed is the same for all wavelengths and frequencies Speed of Sound Wave But speed of sound di ers in di erent materials v K sti ness bulk modulus of material in units Pa N m2 density of material in units kg m3 low pressure particles change in volume change in applied pressure volume K high pressure particles In gases the heavier the molecules making up the gas the slower the speed Example Helium atom is about 8 times lighter than air molecules 80 nitrogen and 20 oxygen Speed of sound in helium is 8 2 8 times larger Speed of Sound Wave The speed of sound also depends on temperature 21 C v 344m s increases sound speed by v 331 0 6 temperature in C m s in air at room temperature 1 C increasing temperature by 0 17 Warming up a wind instrument changes speed of sound and this a ects the pitch Exercise A ute is stored in a cool place at but in the process of playing 15 C it the utist warms it up to 30 C What is the speed of sound at the respective temperatures By what fraction has the speed of sound changed