Please wait for the animation to completely load.

A positive test charge is shown in the animation. You can add positive and/or negative charges. All charges are added to the middle of the animation, so you must drag each newly added charge to a new location. When you push "play," the test charge will move under the influence of the forces from the other charges. Restart.

1. Add one positive charge. Describe and explain the motion of the test charge.
2. How can you tell from its motion that the test charge experiences a force, but that the force decreases as the test charge moves away from the positive charge?
3. What do you predict the motion will be if the positive charge is replaced by a negative charge?
4. Clear the screen and try it. Was your prediction correct?
5. How can you configure two charges of the same sign and keep the test charge stationary? Describe your configuration.
6. What happens if you move one of the charges slightly? This is a demonstration of an unstable equilibrium point (like a gymnast on a balance beam; nudge her one way or the other and she will fall).
7. Design and describe a configuration in which the test charge will oscillate back and forth.
8. Explain why (in terms of the forces) the test charge oscillates in your configuration.
9. Clear the charges and add one negative charge. Let the test charge start moving (so it has an initial velocity) and then move the negative charge around so that the test charge orbits the negative charge. Explain (in terms of forces) why it orbits.