## Exploration 22.5: Pendulum Electroscope

Two identical balls are hung pendulum-like in a laboratory as shown  (position is given in meters and time is given in seconds). The charge on each ball, in mC, can be varied by using the slider. Position can be measured by click-dragging. Restart.

1. Is there any difference in behavior if the on both balls charge is changed from negative to positive?
2. Notice that you can zero the velocity. Can you find a spot where the balls are in equilibrium? (You may need to set the velocity to zero several times to get the balls in equilibrium.)
3. What is the mass of each ball? (Assume that the charge on the two balls is uniformly distributed.)
4. How large a charge is required for the angle (as measured from the pivot) between the two balls in equilibrium to be 90 degrees? How large a charge for 180 degrees? Physlets were developed at Davidson College and converted from Java to JavaScript using the SwingJS system developed at St. Olaf College.

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