The Physics of War: Chris Kyle's Bullets

American Sniper is a movie directed by Clint Eastwood, based on the autobiography of former soldier Chris Kyle. Bradley Cooper, playing the role of one of the deadliest American SEALs, joins the army as a sniper to fight in Iraq. The experiences he will have on the battlefield will condition him psychologically to the point of causing concern in his family. However, his deeds in battle amaze fellow soldiers who look at him as a hero. For this reason, Chris will be forced to choose between his family and the battlefield.

The soldier proves to be very effective in action as a sniper. Before shooting, Chris is aware that he must take into account many important factors such as the wind and the position of the enemy. Another key factor is the effect of the Coriolis force, capable of deflecting the projectile in its trajectory.

Let's see what is the origin of this force.

Coriolis force influences also the motion of cyclones.

A projectile, moving within a rotating reference frame (the Earth), is subject to two pseudo forces: the centrifugal force and the Coriolis force. The first is well known and is what we experience when, in the car, we turn and we feel pushed against the door. On the other hand, when a body leaves the surface of the Earth, it adds to its initial speed, possessed since it was bound to the planet, that of its own motion. Moving in the air, it encounters points that move with different linear velocities. Therefore, the body will be in advance or late with respect to those points. As a result, in the northern hemisphere, the projectile is pushed to the right and, to the left, into the southern hemisphere!

Chris is aware of this pseudo effect and he will use his lethal skills to neutralize any kind of danger.