Here's why:
* Neglecting Air Resistance: We usually assume projectiles are moving in a vacuum, meaning there's no air resistance. Without air resistance, there's no force acting horizontally on the projectile.
* Newton's First Law: Since there's no horizontal force, Newton's First Law of Motion dictates that the object continues to move at a constant horizontal velocity.
* Horizontal and Vertical Motion: The horizontal and vertical motions of a projectile are independent of each other. Gravity only affects the vertical motion, not the horizontal motion.
Important Note: In real-world scenarios, air resistance does play a role. Air resistance will slow down the projectile's horizontal motion, causing the x component of velocity to decrease over time. However, in most introductory physics problems, air resistance is neglected.
