Velocity describes both the speed and direction of an object's motion. It is a vector quantity, meaning it includes information about both how fast something is moving and where it is going.
When you walk and drop your keys, the keys inherit your forward velocity at the moment of release. Thus, they have two components of motion - forward and downward.
The forward velocity is what you initially impart to the keys, and it doesn't change because gravity acts vertically, not horizontally. Meanwhile, the velocity changes vertically due to gravitational acceleration.
- Horizontal velocity: Constant due to the inertia of the keys.
- Vertical velocity: Increases steadily due to gravity.
Understanding velocity is key to predicting where and how an object will move, which in this case, tells why the keys land slightly behind the release point but appear to fall straight down from our perspective.