Here's why:

* Centripetal force is a force that acts towards the center of a circular path. It's what keeps an object moving in a circle.

* Projectiles typically follow parabolic paths. This means their motion is not circular, but rather a curve determined by gravity.

When is a projectile affected by centripetal force?

The only time a projectile experiences a significant centripetal force is when it's moving in a circular or curved path due to factors other than gravity. For example:

* A ball on a string being swung in a circle. The tension in the string provides the centripetal force.

* A satellite orbiting the Earth. The gravitational force between the satellite and the Earth acts as the centripetal force.

When a projectile is only affected by gravity:

* The force of gravity acts downwards, not towards the center of any circular path. This means gravity does not provide a centripetal force.

* The projectile's path is a parabola, not a circle.

In summary:

While projectiles can be affected by centripetal forces in specific scenarios, the typical projectile motion under the influence of gravity alone does not involve centripetal force.