Question

When you lift a book from the ground to your desk, what kind of work do you do, negative or positive? by lifting the book, what do you change? Does the book gain or lose energy? What kind of energy?

Answer 1

When you lift the book, you are doing positive work, because the force you exert on it is in the same direction as its displacement. Gravity is doing negative work.

As you lift the book you are increasing the object's gravitational potential energy.