Quantities that are *generally* zero:
* Horizontal acceleration (a_x): In ideal projectile motion, we ignore air resistance. This means there's no force acting horizontally, and therefore no horizontal acceleration.
Quantities that are *sometimes* zero:
* Vertical velocity (v_y): At the very top of the projectile's trajectory, the vertical velocity momentarily becomes zero. This is the point where the projectile changes direction from going up to going down.
Quantities that are *never* zero:
* Horizontal velocity (v_x): In ideal projectile motion, the horizontal velocity remains constant throughout the flight. This is because there's no horizontal force acting on the projectile.
* Vertical acceleration (a_y): Due to gravity, there's always a constant downward acceleration of approximately 9.8 m/s².
Important Note:
* These descriptions apply to *ideal* projectile motion, where air resistance is ignored. In real-world scenarios, air resistance can affect horizontal velocity, making it gradually decrease.
