Some leaves are separated from the tree if we move the tree branch quickly. It is the result of:

Unless acted on by an external force, Newton's first law of motion, often known as the law of inertia, asserts that an object at rest remains at rest and an object in motion remains in motion with the same velocity.

Both the leaves and the tree are initially at rest. When the tree is vigorously shaken, however, the tree moves while the leaves remain stationary. If we vigorously shake a tree's branch, some leaves may become detached as a result of remaining in a resting position.