Everyone's favorite clacking desktop amusement has been weaponized. Well, almost: researchers at CalTech have used Newton's Cradle as a jumping off point for an acoustic weapon capable of ripping through a submarine with its sonic bullets.
The concept is similar: 21 parallel rows of ball bearings, each with weights attached to the end. The drop another ball on the end of a row, and watch the compression wave build. It's what happens when you get to the end of the line that differentiates an ExecuToy from a murder machine:
But unlike Newton's cradle, the system doesn't let the last ball carry the compression wave outward; rather, the energy is passed into the metamaterial, which tightly focuses the waves to a spot a few inches away from the acoustic lens. The researchers were able to focus all of the sound into a very small area, and in doing so they amplified the waves more than 100 times beyond what previous metamaterials have achieved.
Sound bullets have the dual advantages of being able to travel through air, liquids, and solids alike, and of being ridiculously awesome, conceptually. Even better: they can be scaled up to submarine-destroying levels, or down for fuzzier, friendlier medical purposes. Hypothetically, sound bullets could even someday be used to kill off tumors.