What force prevents a book on a table from accelerating downward due to gravity?

The force that prevents a book on a table from accelerating downward due to gravity is the normal force. When an object, like a book, is resting on a surface, it experiences a downward gravitational force due to its weight. In response to this weight, the surface exerts an upward force known as the normal force. This force acts perpendicular to the contact surface of the book and the table.

In a state of equilibrium, where the book does not move, the normal force balances the gravitational force acting on the book, leading to zero net force in the vertical direction. This balance results in no acceleration, keeping the book at rest on the table. Thus, the normal force is crucial in counteracting the gravitational pull, allowing the book to remain stationary.