The answer to this question should be a gravitational force.
A gravitational force is something that sort of attracts two things of mass. This force must never ever pull the objects of mass apart. It must always try to pull them together. So, judging by the question we can tell that the two masses in this situation are the leaf and the ground. When the leaf fell on the ground this was the gravitational force pulling the leaf down so it connects with the ground.
- Marlon Nunez