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let's first take a look at what's inside a bullet. Did you realize that they're designed a bit like fireworks? Most bullets consist of three basic parts: the primer, the propellant, and the bullet metal itself. The primer, sometimes called the percussion cap, is like the fuse. When a gun's trigger is pulled, a spring mechanism pushes the firing pin into the back of the bullet, where it ignites a small explosive in the primer. This, in turn, ignites the propellant, which is the main explosive that takes up about two thirds of a typical bullet's volume. The propellant chemicals burn at a steady rate, building up lots of gas pressure very quickly in order to push the bullet metal down the gun barrel and through the air to the target. These explosions that power the bullet occur inside the small gun barrel. When the bullet leaves the end of the barrel, all the pressure of the explosions is released suddenly, resulting in the loud sound you know as gunfire. When bullets fly through the air, they do so at amazing speeds. The fastest bullets travel more than 2,600 feet per second. That's equivalent to over 1,800 miles per hour. To put that in perspective, it's amazing to realize that bullets travel over twice the speed of sound! If you shoot a gun at a target several yards away, it's easy to think of bullets traveling in a straight line. In fact, over very short distances, bullets do more or less follow a straight path. Over longer distances, though, a bullet's path is much more complicated due to several forces. The inside of a gun barrel has spiraling grooves, known as rifling, cut into it. These grooves make bullets spin very fast as they emerge from the barrel. This spinning motion makes a bullet somewhat like a gyroscope, helping it to travel as straight as possible to reach its intended target. Along the way, however, several forces act on a bullet to make its path more complicated. First, gravity pulls on a bullet, making its overall path a slight downward arc. In addition, the air provides resistance and the recoil from firing a gun also can send a spinning bullet on a slightly wobbly path. When you combine all these forces, a bullet's path is a bit like a complicated corkscrew shape!