For information on how to use the applet on the left, please go to Applet Help on the applet's Help menu.

In each of the four applet panels on the left, a particle is displayed (red object). In each panel except one, the particle is interacting with one or more other objects. The other object(s) is(are) not shown.

Question. In which of the four motions does the red particle not interact with another object?

Select (a), (b), (c), or (d) below, and then click GO for a discussion of that situation.