Scientific reading and explanation
Potential energy belongs to a configuration
A book held above a floor has gravitational potential energy because of the configuration of the Earth–book system. Gravity can transfer energy to motion as the book moves down. The book's mass alone does not locate all that stored energy; the Earth–book interaction matters. A spring stores elastic potential energy in its deformation as well.
Choose a reference before calculating
Near Earth's surface, when gravitational field strength g can be treated as constant, changes in gravitational potential energy follow ΔU_g=mgΔh. With a reference height h=0, we often use U_g=mgh. The numerical value of gravitational potential energy depends on the chosen zero; observable changes do not. Heights and displacements are not interchangeable without a defined vertical direction.
Do not mistake conservation for static motion
In a closed idealized system, gravitational potential energy can decrease as kinetic energy increases. The total energy can remain constant while the separate bars change. For a 2 kg object at 5 m, choosing floor height as zero, U_g=2×9.8×5=98 J. That does not imply the object is already moving.
System boundaries are essential
If we choose only the falling object, Earth's gravity performs external work on it. If we choose the Earth–object system, gravitational potential energy is an internal system property. State the boundary before writing a conservation claim. Our synthetic model uses a uniform near-Earth gravitational field and no contact impacts.