Everyone knows what a sword is, whether it be a katana, claymore, or even the famed Excalibur of Arthurian tales. Sure when you swing a sword it cuts, but what about the sound it makes? This came to mind as I thought of one of my favorite movies, The Last Samurai. At first I related it to the sounds produced by whips or arrows, but I wanted to look into the matter to find out what is really behind the cause of a sword's sound.
To go with the theme from The Last Samurai, I researched a lot about the ideas the Japanese associate with their swords. in Japan in order to have a proper sound, or hasuji, the blade must create the proper sword wind, or tachikaze. When a sword slices through the air, it must push away air molecules and creates what is called a thickness noise. This works in conjunction with loading noise, which is the blade having a direct effect on the air, generating forces to move it about. Since the blade of a katana is tapered, this allows it to cut the air more aerodynamically, and forms a vortex of air behind it, What you hear is the tone of the blade cutting through and pushing molecules out of the way, much like an arrow piercing the air as it flies by.