Part 2/10:
To understand this potential transformation, we first need to address the concept of inertia regarding confined energy. When we consider an object with mass, its resistance to changes in motion is fundamental. An object accelerates only when acted upon by an external force. This innate persisting tendency is not only mechanical; it relates to the very essence of energy.
Consider a block of material in the vacuum of space. To change its state of motion, a force is required. In a gravitational field, objects also exhibit a push and pull towards each other. Here, we see an essential equivalence. From Einstein's principle of relativity, inertial mass and gravitational mass are fundamentally the same, underpinning the association between them.