sound

what we hear as sound

is but vibrations in the air all around

the vibrations once ticked

travel as waves acoustic

which be longitudinal in fashion

the medium vibrates in the wave's direction

a medium is of prime essence

for no acoustics in medium's absence

and it be an important difference

between this and waves of luminescence.

imagine a long constrained spring
pull one end and watch the wave speeding
the wave be made of two sections

regions of compression and rarefaction
that put together occupy a wavelength
and two characteristics to convey its strength -
pitch be the effect of frequency
multiplied with wavelength gives the wave's speed
expressed in the honor of Hertz Heinrich
just a count of the cycles that in a second creep.

loudness be decided by the intensity

which is just a simple property

determined by the wave's amplitude

which is how much a particle moves

its level is expressed in decibels

which honors the old Graham Bell

and 'tis for just this reason, you see

that it is dB ( not db )

'coz units named after people 

are abbreviated with capital.

just like with all the waves
there's also a thing called phase
which is but a measure of

relative shift in the stage

only of use when more than one

they result in interference patterns

then there's this interesting part

cars change pitch when they pass

because relative motion impacts the frequency

Doppler shift maps the motion with great decency.