Why does only vertical force affect the motion of projectiles?

In my physics class, we learned that only vertical forces, not horizontal forces, affect the motion of projectiles. I'm having difficulty understanding why this is true. Can someone explain to me how or why horizontal forces don't affect the motion of projectiles?Why does only vertical force affect the motion of projectiles?Any force can affect the motion of projectiles. In HS phyics problems, only gravity(a vertical force) is considered for the purposes of simplicity. In the real world, air, spin drift(in the case of rifled projectiles), coriolis effect and others affect the motion of projectiles, which aren't vertical forces.Why does only vertical force affect the motion of projectiles?Not quite. Vertical motion affects how long the projectile is in the air, because acceleration is in the vertical direction. Horizontal motion tells you how far the projectile will go, because the horizontal motion will continue unchanged as long as the projectile is in the air.



It stops moving when it hits the ground or some other obstacle, and generally that timing is determined by the vertical motion. If it never moved downward, it would never hit the ground.