A book is placed on a dashboard of a car that is stopped at a traffic light. As the car starts to move forward, the book slides off the dashboard. Pick the most correct explanation for the book sliding off the dashboard. A. There is grease on the dashboard, so the book slides off the dashboard. B. Due to inertia, the book slides off the dashboard. C. The book is heavy, so it slides off the dashboard. D. Air resistance made the book move backward.

Inertia is a fundamental concept in physics. It refers to the property of an object that resists any change to its state of motion. In simpler terms, if something is at rest, it wants to stay at rest. If something is moving, it wants to keep moving at the same speed and direction. This resistance to changing motion is due to the object's mass.

When you placed a book on the dashboard of a stationary car, the book remains at rest due to inertia. If the car suddenly starts moving, the book does not immediately follow the car's motion. Instead, it tends to stay in place (relative to the ground), while the car moves forward from under it. This gives the appearance that the book is sliding backward. This is why option B in the given exercise is correct—the book slides off due to inertia.

Newton's First Law of Motion, often called the Law of Inertia, states that an object will remain at rest or move in a straight line at a constant speed unless acted upon by an unbalanced force. This principle is crucial in analyzing the behavior of the book on the car’s dashboard. When no external force acts on the book, its inertia keeps it at rest.

But when the car starts moving (applying a force), the book initially stays in its rest state due to inertia. However, the car’s motion is an unbalanced force. Eventually, friction between the book and the dashboard would pull the book in the same direction as the car, but if the car's acceleration is swift, the book does not get enough time to 'catch up' and slides off.

Understanding Newton’s Laws helps explain why the book remains stationary relative to the ground and why it appears to slide backward from the car’s perspective.

An unbalanced force is required to change the motion of an object. In the car-book scenario, the force from the car’s acceleration is unbalanced in relation to the book. Initially, the book has no force acting on it, so it stays put (inertia).

As the car accelerates, the dashboard moves forward, but the book resists this change in motion. The friction force between the book and the dashboard is not enough to keep the book in place, leading to the unbalanced force condition. As a result, the book falls off the dashboard.

This situation highlights how unbalanced forces affect objects differently, depending on their interaction with the surfaces they're on and other forces (like friction). Understanding how unbalanced forces work clarifies why the book behaved as it did—staying at rest until the car's rapid movement created an imbalance, causing it to slide.