Making sounds virtual G. Karwasz, L. Gratton, E. Rajch Dipartimento di Fisica, Università di Trento, Italy and Pomorska Akademia Pedagogiczna, Słupsk, Poland

Sounds Sounds, i.e vibrations

Everything plays Depending on the source and the mode, the whole variety of sounds can be generated What makes the difference between them: why some of them are pleasant, other sharp or dull? · Can we see the variety of these sounds? freeware Oscilloscope 2.51 (K. Zeldovich). The program allows visualization of registered sounds and their Fourier analysis

Sound wave The fundamental quantity describing a simple sounds – a monocromatic sine wave are the frequency, length and velocity of propagation. 

Glass music In practice, generating a single frequency is not easy. Surpisingly, monocromatic sounds are generated by glasses. What determines the frequency of glass?

Glass music

Blow instruments Sounds can be generated in different type tubes and whistles. Also bottles can play. The “pitch” of the sound, first of all depends on tube length. But the pitch depends also on the power in the blow P= ½ vρω2A2 where v is the sound velocity, ρ gas density, ω – frequency, A – amplitude of the wave

Trumpets Infinite ways to generate sounds in tubes of variable length.

Flutes Infinite ways to generate sounds in tubes of variable length.

Closed flute W piszczałce zamkniętej fala stojąca ma na jednym końcu węzeł, na drugim strzałkę

Open flute In open tube knots are formed inside. Frequencies scale like 1:2.3 etc. i.e. “octave” intervals But: 1) even the ligthest blowing generates higher harmonics 2) Exact scaling does not hold for the strongest blow – the dominating frequency belongs to the “closed tube” series

Strings The frequency of the strings depends on the tension F, mass linear density  and string length l.

Sounds of a rod A metal rod creates a variety of sounds, depending on the mode of excitation. In the rod, these are longitudinal waves which give the sound

Psalm book from Reims cathedral, now in St John’s College, Cambridge Evil’s music As seen from this XIth century psalms book, vibrations of mebranes are much more complex than those of strings. Psalm book from Reims cathedral, now in St John’s College, Cambridge

Thunder drums

Painful noise

“White” noise White noise, differently from “glass music” has a wide spectrum of frequencies. Waterfalls is a good example.

Physics is fun http://if.pap.edu.pl