Relationship between a conservative force F and the potential energy U it creates:
As with momentum, the energy of an isolated system is always conserved. It might change form—
potential energy can be converted to kinetic energy, or kinetic energy can be converted to heat—but it’ll
never simply disappear.
Conservation of energy is one of the most important, fundamental concepts in all of physics ...
translation: it’s going to show up all over the AP exam. So read this chapter carefully.
Kinetic Energy and the Work-Energy Theorem
We’ll start with some definitions.
What this second definition means is that work equals the product of the distance an object travels and the
component of the force acting on that object directed parallel to the object’s direction of motion. That
sounds more complicated than it really is: an example will help.
A box is pulled along the floor, as shown in Figure 14.1 . It is pulled a distance of 10 m, and the force
pulling it has a magnitude of 5 N and is directed 30° above the horizontal. So, the force component that is
PARALLEL to the 10 m displacement is (5 N)(cos 30°).
Figure 14.1 Box is pulled along the floor.One newton·meter is called a joule, abbreviated as 1 J.• Work is a scalar. So is energy.