Instructions: Based on the information present in the given passage, you need to write a correct answer to the given question. A correct answer is one that correctly and completely answers the question. Do not write answers that address the question partially or incorrectly. The correct answer must be contained in the given paragraph.
Input: Paragraph- Sent 1: In many parts of the world, trees lose their leaves in autumn.
Sent 2: The leaves turn color.
Sent 3: Then fall from the trees to the ground.
Sent 4: As the leaves are falling, they have kinetic energy.
Sent 5: While they are still attached to the trees they also have energy.
Sent 6: When they are attached they are not in motion, so how can they have energy?
Sent 7: Instead of kinetic energy, they have stored energy.
Sent 8: This stored energy is called potential energy.
Sent 9: An object has potential energy because of its position.
Sent 10: For example, leaves on trees have potential energy because they could fall.
Sent 11: They fall because of the pull of gravity.
Sent 12: Potential energy can be transferred into motion.
Sent 13: Motion can also be turned back into potential energy.
Sent 14: Objects have potential energy due to their position.
Sent 15: A leaf on a tree branch has potential energy.
Sent 16: The leafs energy can be turned into motion as it falls.
Sent 17: Once the leaf is on the ground, it has no more potential unless it is lifted back up. 
Question: How does potential energy exist and change?.
Output:
Through gravity.