One example of the law of inertia is that a package thrown from a plane will move as fast as the plane in the same direction. The law of gravity affects the package, and while the horizontal axis speed is the same as the plane, the vertical axis speed increases.
The law of inertia states that an object that is already moving will continue to move and the speed of the movement remains the same. The only factor that can change the speed or the direction is an unbalanced force. In a state of motion, all objects are able to resist changes.