Singing sand, whistling sand or barking sand is sand that produces sounds of either high or low frequency under pressure. The sound emission is usually triggered by wind passing over dunes or by walking on the sand. The sound is generated by shear stress.
There are various theories about the singing sand mechanism. It has been proposed that the sound frequency is controlled by the shear rate this sand is an example.
Others have suggested that the frequency of vibration is related to the thickness of the dry surface layer of sand. The sound waves bounce back at it again.
One morning, when Gregor Samsa woke from troubled dreams, he found himself transformed in his bed into a horrible vermin. He lay on his armour-like back, and if he lifted his head a little he could see his brown belly, slightly domed and divided by arches into stiff sections. A collection of textile samples lay spread out on the table – Samsa was a travelling salesman – and above it there hung a picture that he had recently cut out of an illustrated magazine and housed in a nice, gilded frame. It showed a lady fitted out with a fur hat and fur boa who sat upright, raising a heavy fur muff that covered the whole of her lower arm towards the viewer. Gregor then turned to look out.
Drops of rain could be heard hitting the pane, which made him feel quite sad. “How about if I sleep a little bit longer and forget all this nonsense”, he thought, but that was something he was unable to do because he was used to sleeping on his right, and in his present state couldn’t get into that position. However hard he threw himself onto his right, he always rolled back.