Horizontal vs. Vertical Motion: A lot of students get mixed up between horizontal and vertical motion.

• Horizontal motion happens at a steady speed.

• Vertical motion is affected by gravity, which pulls things down at about 9.81 meters per second squared.

Independence of Axes: Horizontal and vertical motions do not depend on each other.

• For example, how long something stays in the air depends only on its vertical motion.

Effect of Air Resistance: Many people forget about air resistance when thinking about how things move.

• Air resistance can change how things travel, making them go differently than what you might expect.

Range Formula Misunderstanding: The formula for the range ($R$) in projectile motion is:

$R = \frac{v_0^2 \sin(2\theta)}{g}$

• This formula only works in a vacuum, where there’s no air resistance.