How can we hear the sea in a shell?

Sad to say, it isn’t really the sea which you can hear when you hold a shell up to your ear, even though it may sound exactly like it. What is really happening is this… All sounds move through the air on vibrations of air called sound waves. We cannot see sound waves moving, but even the tiniest sounds being made in a room will have their own sound waves. There is air too, of course, in the spiral cavity inside the shell, and when sound waves enter they make this air vibrate as they bounce backwards and forwards off the inner wall of the shell. The result is a deep rumbling sound from the air which is resounding inside the shell. This sound reminds us of the sound of waves beating on a shore. It is in just the same way as this that air, vibrates inside the ‘resonator’, of musical instruments, making the sounds of the notes being played.