when you lift a book of 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 loose energy? what kind of energy?
It would be kinetic energy. Let's say the book is weighs 10 Newtons you need to use a force of 10 Newtons to lift the book. In other words it's positive. As you move the book you're giving it energy. Namely potential energy which will turn to kinetic energy if you let it go. So you're changing it's position and energy.
