1. Gravity: This force acts vertically downwards, causing the projectile to accelerate downwards.

2. Initial Velocity: This is the force that propels the projectile in a specific direction. It's the initial push or throw that sets the projectile in motion.

While the projectile is in motion, there are no other forces acting on it (ignoring air resistance). The initial velocity and gravity combine to create the curved path that we recognize as projectile motion.