* Gravity only affects the vertical motion: Gravity acts downwards, solely affecting the vertical velocity of the object. It causes the object to accelerate downwards, making its vertical velocity increase over time.

* Horizontal velocity remains constant: In the absence of air resistance, there's no force acting horizontally on the object. Therefore, the horizontal velocity stays the same throughout the object's flight.

Here's a simple example:

Imagine throwing a ball horizontally. The moment you release the ball, it has an initial horizontal velocity. This velocity will remain constant throughout the flight.

At the same time, gravity starts acting on the ball, pulling it downwards. This results in an increasing vertical velocity, making the ball follow a curved path (a parabola).

In summary:

* Horizontal velocity: Constant, unaffected by gravity.

* Vertical velocity: Changes due to gravity, increasing downwards.

Important Note: This is a simplified model that doesn't consider air resistance. In reality, air resistance will affect both the horizontal and vertical velocities, but it's a more complex factor to consider.