Physics

Indiana Jones and the Crystal Skull was, like other Indiana Jones movies, fun but not realistic. Hollywood movies usually get physics completely wrong, so when I go to movies I usually just turn off the physics portion of my brain and enjoy the story.

There was one scene in this movie, however, where they got the physics right. In one of the many death and credibility defying escape/chase scenes the old professor was riding in the back holding the precious crystal skull. They went over a bump and his treasure flew vertically upward. When it fell back down it landed right in his lap. That may seem unrealistic but the physics was exactly right. It was perhaps the most realistic portion of the chase and certainly more realistic than a sixty something archeologist doing all those death defying stunts.

Why should the skull fall right back into the old professor's lap? A fundamental principle of two dimensional motion is that the vertical and horizontal motions are completely independent of each other. Vertical motions have no effect on the horizontal motion and vice versa. When you are driving in a car and throw something straight up, the change in its vertical motion has no effect whatsoever on the horizontal motion. The horizontal speed remains the same as the vehicle's speed, so relative to the car and passengers the object seems to go straight up and down. As long as the driver does not accelerate, brake, or turn it will fall back down right on top of you. (neglecting wind effects)

The skull therefore falls right back into the old professor's lap in a rare, for an Indiana Jones movie, realistically possible scene.