In recent years, the ancient eastern art of Karate-Do (a Japanese word, literally translated as “the way of the empty hand”) has become popular in the western world. Karateka—practitioners of Karate—often break boards, cinderblocks, and other solid materials in order to demonstrate the strength that their training develops. Much can be said of the history and culture associated with the expansion of martial training, but this essay—it is, after all, a physics paper—will examine the collision mechanics of a hand strike to a solid target like a board. 2 Force, Momentum, and Deformation Energy That large objects moving at high speeds hit harder than smaller objects moving more slowly goes without saying. In attempting to break a board, a karateka seeks to hit the board as hard as possible. It therefore follows that the karateka should move his or her weapon (for the purpose of this paper, the hand) as quickly as possible in order to hit as hard as possible. But what makes for a “ha...
