Final Answer:
The form of energy represented by books lying on a desk is potential energy, specifically gravitational potential energy. When a book falls off a desk, the energy changes to kinetic energy as it moves.
Step-by-step explanation:
The books on the desk possess potential energy due to their position relative to the Earth's surface. This potential energy is a result of gravity acting on the books, given by the formula PE = mgh, where PE is potential energy, m is the mass of the book, g is the acceleration due to gravity, and h is the height of the book above the ground. When the book is on the desk, it has potential energy as it's at a certain height above the ground level.
As the book falls off the desk, its potential energy begins to convert into kinetic energy, the energy of motion. The kinetic energy of an object in motion is given by KE = 0.5 * m * v², where KE is kinetic energy, m is the mass of the book, and v is the velocity of the book as it falls. As the book descends, its potential energy decreases while its kinetic energy increases, as gravity accelerates it toward the ground.
The transition from potential energy to kinetic energy is a conversion between energy forms, as the book's position changes, leading to a change in its energy state. Initially possessing gravitational potential energy due to its elevated position, the book's transformation into kinetic energy occurs as it accelerates towards the ground under the influence of gravity, demonstrating the interconversion of energy forms in this scenario.