16.1. Reviewing Gravitational Potential Energy http://www.ck12.org
16.1 Reviewing Gravitational Potential Energy
Objectives
The student will:
- Review gravitational potential energy.
- Understand gravitational potential.
Vocabulary
- gravitational potential:The potential energy per unit mass, represented byVg.
Introduction
Earlier, we compared Newton’s law of universal gravity with Coulomb’s law. In this chapter, we will use gravita-
tional potential energy to draw an analogy with electrical potential energy. Let us begin by reviewing gravitational
potential energy.
A Review of Gravitational Potential Energy
If we remain close to the surface of the earth, the gravitational accelerationgis considered constant. The gravitational
potential energy of an object then increases if we lift it higher. We have done work on the object and increased the
potential energy of the object. The Earth, however, has done negative work on the object, because as the object is
lifted, the force on the object due to gravity is opposite to the object’s displacement,Figure16.1. Conversely, if the
object is dropped, its potential energy decreases, but the work done by gravity is positive, because the force on the
object due to gravity is in the same direction as the object’s displacement,Figure16.2.
FIGURE 16.1
Object is lifted. The change in PE is positive but the work done by gravity
is negative.