The horizontal and vertical motion of the object are independent (except for the total time). The vertical acceleration is constant (at –9.8 m/s 2 ). The horizontal velocity is constant.

But here's the bit that justifies Dawson's explanation of projectile motion. Basically, a projectile like a golf ball has two velocity components, a horizontal one and a vertical one, as Martin ...

Horizontal Projectile Motion As the name suggests, horizontal motion occurs when the object is thrown horizontally, meaning it starts with zero vertical velocity.

First, it shows that the horizontal and vertical motion in projectile motion are independent. That is, what happens in the y-direction, stays in the y-direction.