Pith Ball Lab


Pith balls with positive, negative, or no electrical charge are suspended from strings. The charge and mass of the pith balls can be adjusted, along with the length of the string, which will cause the pith balls to change position. Distances can be measured as variables are adjusted, and the forces (Coulomb and gravitational) acting on the balls can be displayed.

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Assessment Questions (5):

  1. For the image below, which values for the charges on the two pith balls could be correct?

    Attracted pith balls
  2. In the experiment shown below, which is greater, the force of gravity on the pith balls (Fg) or the electrostatic force between them (Fq)?

    Repelled pith balls
  3. For a pith ball experiment set up on Earth, which image below correctly depicts the result if you gave the left-hand pith ball a charge of +7.0 × 10−6 C and the right-hand pith ball a charge of +11.0 × 10−6 C? Assume the pith balls have equal mass.

    4 possible pith ball results
  4. In a pith ball experiment, the two pith balls are at rest. The magnitude of the tension in each string is |T| = 0.55 N, and the angle between each string and a vertical line is θ = 27.33°. What are the values for the magnitudes of electrostatic force, Fq, and the gravitational force, Fg?
  5. One object has a charge of +5.0 × 10−6 C, and a second object has a charge of +2.0 × 10−6 C. The objects are 0.5 meters apart. What is the electrostatic force between them?

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