* Air resistance is proportional to velocity: The faster an object moves through the air, the more air molecules it collides with per unit time. This leads to a greater force opposing the object's motion.

* Drag force equation: The basic equation for drag force is:

* F_d = 1/2 * ρ * v^2 * C_d * A

* Where:

* F_d is the drag force

* ρ is the density of the air

* v is the velocity of the object

* C_d is the drag coefficient (depends on the object's shape)

* A is the object's cross-sectional area

Important Points:

* Terminal velocity: As an object accelerates, the drag force eventually equals the force of gravity. At this point, the net force on the object is zero, and it stops accelerating. This is called terminal velocity.

* Drag is not constant: Drag is not a constant force. It increases as the object's speed increases, following the square of the velocity.

Example:

Think about a skydiver. When they first jump out of a plane, they accelerate rapidly. As they speed up, air resistance increases dramatically. Eventually, the drag force becomes equal to the force of gravity, and the skydiver reaches terminal velocity (around 120 mph).