* Gravity is constantly doing work on the book: Gravity pulls the book towards the center of the Earth. If you hold a book up, you are doing work against gravity to keep it from falling. Even when it's resting on a table, gravity is still pulling on the book.
* Forces from the environment: The book might experience air resistance (especially if it's moving), or forces from the surface it's resting on. These forces can be doing work on the book.
* Work done by you: If you pick up a book, move it, or put it down, you are doing work on the book by applying a force and causing it to move.
* Internal work: The book itself might be undergoing internal changes, such as molecules moving around, which could also be considered work being done.
The key to understanding work in physics is to remember the following:
* Work is done when a force causes displacement. Displacement means a change in position.
* Work can be positive or negative: Positive work is done when the force and displacement are in the same direction. Negative work is done when they are in opposite directions.
So, while a book might not be visibly moving, there are many forces acting on it, and thus work is being done on it in various ways.
