You are working in a library, reshelving books. You lift a book from the floor to the top shelf. The kinetic energy of the book on the floor was zero, and the kinetic energy of the book on the top shelf is zero, so there is no change in kinetic energy. Yet you did some work in lifting the book. Is the work-kinetic energy theorem violated?
1.Yes, it is violated because a force acting on the book should change the book's kinetic energy.
2.No, it is not violated because the book really does have a final velocity, but so does the entire system, so it is impossible to detect the book's motion.
3.Yes, it is violated because a force that acts on the book should change the book's velocity.
4.No, it is not violated because there are two forces that act on the book. One is the downward force that the Earth exerts on the book, which is counterbalanced by the upward force that you exert on the book. The total work done on the book, therefore, is zero, and is equal to its overall change in kinetic energy.
Question 2
If 3 different conservative forces and one non-conservative force act within a system, how many potential energy terms appear in the energy equation that describes the system?
1.0
2.1
3.3
4.4
Lycopodium obscurum growing on the forest floor.
British Library
Correct position when lifting a heavy object off the floor.
Three toddlers sit on the floor playing with a toy.
St. Matthew, from the Gospel Book of Charlemagne.
Head-tilt, chin-lift maneuver.