What two forces act on a bullet's trajectory after it leaves the rifle barrel?

The correct answer identifies the two primary forces acting on a bullet's trajectory after it exits the rifle barrel: gravity and the force due to air flow, which is generally understood as drag.

Gravity is a constant force that acts downward on the bullet from the moment it leaves the barrel. This force pulls the bullet towards the earth, influencing its vertical drop over distance. As the bullet travels, it will experience a downward arc due to this gravitational force.

The second force, often referred to as drag or air resistance, results from the bullet moving through the air. This resistance opposes the bullet's forward motion and can significantly affect its velocity and trajectory. The air molecules collide with the bullet, creating a drag force that slows it down as it travels. The shape and speed of the bullet, along with environmental conditions like air density, will influence the amount of drag it experiences.

Recognizing the impact of both gravity and air drag is crucial for understanding bullet trajectories in ballistics, as they are the primary factors that alter the path of a projectile once it is in flight. Other options listed, such as wind resistance and centrifugal force, may contribute under certain conditions but do not encompass the entire scope as accurately as gravity and drag.