* Potential energy: This is stored energy due to an object's position or state. When the book is held above the floor, it has gravitational potential energy because of its height.

* Kinetic energy: This is the energy of motion. As the book falls, it gains speed and therefore gains kinetic energy.

The process:

1. Initial state: The book is at rest, with potential energy stored due to its height.

2. Falling: Gravity pulls the book downwards, causing it to accelerate and gain speed.

3. Conversion: The potential energy the book had is gradually converted into kinetic energy as it falls.

4. Impact: When the book hits the floor, its kinetic energy is transferred to the floor and dissipated as heat and sound.

In essence, the book's potential energy is not lost, but transformed into another form of energy (kinetic) during its fall.