1. Gravity: This is the force that pulls the projectile downwards, causing it to follow a curved path.

2. Air Resistance (Drag): This is the force that opposes the motion of the projectile through the air. It acts in the opposite direction to the projectile's velocity.

While gravity is always present and acts vertically downwards, air resistance is a more complex force that depends on factors like the projectile's speed, shape, and the density of the air.

Note: In many simplified projectile motion problems, air resistance is ignored to make calculations easier. However, in real-world scenarios, air resistance plays a significant role, especially at high speeds.