A: The concept of work

The work W done on an object by a constant force is defined as W = F·d.  It is equal to the magnitude of the force, multiplied by the distance the object moves in the direction of the force.  The SI unit of work is Nm = J,

B: Work and the electric field

In the diagram below the red dot denotes a positive point charge.  Points W, X, Y, and Z and the point charge lie in the same plane.  Points W and Y are equidistant from the charge, as are points Y and Z.

C: Electric potential difference

A potential energy function is a function of the position of an object.  It can be defined only for conservative forces.  A force is conservative if the work it does on an object depends only on the initial and final position of the object and not on the path.

Suppose the charge in part B increases from +qe to +1.7 qe.

When a net force does work on an object, its kinetic energy changes.
Wnet = ½m(vf2 - vi2) = ∆K.

Go to Blackboard, Assignments, and answer the questions for Extra Credit 4.