Does gravity cause a change in velocity? why?
Yes it does.
Gravity is applied to every single thing on Earth and changes from place to place, depending on the distance of a body to the center of the Earth.
A force applied to all bodies on Earth is Weight (
If a body is free falling, its only acceleration is
In case of flying or going upwards, weight decelerates a body, reducing its velocity.
If weight is stronger than the rest of the forces applied, then not only will velocity's meter change, but also its direction.