A bow is a flexible arc which shoots aerodynamic projectiles called arrows. A string joins the two ends of the bow and when the string is drawn back, the ends of the bow are flexed. When the string is released, the potential energy of the flexed stick is transformed into the velocity of the arrow. Archery is the art or sport of shooting arrow from bows. Today, bows and arrows are used primarily for hunting and for the sport of archery. Though they are still occasionally used as weapons of war, the development of gunpowder and muskets, and the growing size of armies, led to their replacement in warfare several centuries ago in much of the world. Someone who makes bows is known as a bowyer, and one who makes arrows is a fletcher —or in the case of the manufacture of metal arrow heads, an arrow smith.