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In the realm of physics, the concept of work highlights how forces cause objects to move. Work is defined as the product of the force applied to an object and the distance over which that force is applied. It is given by the formula \( W = F \cdot d \cdot \cos(\theta) \), where \( F \) is the force, \( d \) is the displacement, and \( \theta \) is the angle between the force and the direction of displacement.
In this exercise, the work done by friction is negative because it opposes the book's motion. When you push the book, friction resists by doing negative work, which decreases the book's mechanical energy as it moves.
This example illustrates how energy is transferred from the book's kinetic energy to thermal energy due to friction. The amount of work done depends on the force of friction and the distance, both independent of the path taken. Whether you push the book in a straight line or take a two-part path, the work done by friction remains constant, because the total displacement is the same in both cases.

Forces are what cause changes in the motion of objects, and one of the most common is friction. It acts opposite to the direction of movement, slowing down or completely stopping the motion of objects. Understanding how to balance these forces and predict the resulting motion is a fundamental part of physics.
In this particular exercise, friction is the force of interest. It arises because the surfaces in contact—the table and the book—are not perfectly smooth, creating resistance to motion. Even though it's sometimes regarded as a 'limiting' force, friction is crucial in daily life as it allows us to walk without slipping and cars to stop safely.
By calculating the work done by this force, we understand how much motion is resisted by the friction at play. This understanding helps not only in solving physics problems but also in applications like designing safer transportation systems or creating better sports equipment.

Solving physics problems often involves breaking them into simpler parts and understanding the underlying principles. For this exercise involving friction, the solution requires knowing how friction works and assessing the work it performs.
Start by identifying what information is provided. Here, the work done by friction when pushing the book straight is given and needs to be assessed for a different path. Understanding that friction's resistance is independent of path helps simplify the problem, avoiding unnecessary calculations.
Next, apply known formulas and principles. In this case, because the displacement and frictional force stay the same, the work remains unchanged. This kind of problem-solving is about logical thinking and understanding when certain factors remain constant, aiding in efficient and accurate solutions in physics.