Here's why:

* Gravity: Gravity constantly pulls objects downwards.

* Air Resistance: As an object falls faster, it encounters more air resistance. This resistance acts as an opposing force to gravity.

* Terminal Velocity: When the force of air resistance equals the force of gravity, the object stops accelerating and reaches a constant speed. This is the terminal velocity.

It's important to note that terminal velocity depends on factors like:

* Object's shape: A streamlined object like a bullet will have a higher terminal velocity than a wider object like a parachute.

* Object's mass: Heavier objects have a higher terminal velocity.

* Air density: Terminal velocity is lower in thinner air (like at high altitudes).