Abstract: Ninja Track is a belt shaped object which possesses the capacity to alter its flexibility and hence strength. It consists at its modular level - a composition of two parts - the vertical hinges and horizontal hinges. When flat, Ninja Track is fluid and wavy. When the user folds it at the horizontal hinges, Ninja Track becomes a rigid stick. Using Ninja Track, we had created two applications. One is a physical game interface which can transform a whip into a sword virtually and physically. Another is a musical instrument which can make sounds depending on its shape and interaction.