Bullet design also affects what happens when a bullet hits an object. The way a bullet behaves when it hits a target is called 'terminal ballistics.' The make-up and density of the target material, the angle at which the bullet hits, and the speed and design of the bullet itself are all factors. Bullets are usually made to go into a target, change shape, and/or break apart. For a given material and bullet, the speed of the bullet is the main factor determining what happens.