A natural phenomenom, Known as the force that attracts two objects. It's directly proportional to the mass of the, and is also inversely proportional to the distance between them.
We can conclude , many things. For example, that the gravitational acceleration is the one that can change the velocity of an object that it's dropped from a specific distance. Also That in that case in particular, the velocity has a linear increasing relation with the time, which means that as the time increases the velocity will increase too. And finally that the gradient is the one that can help us to determine the rate of change of any value during time.