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Physics Honors/AP 1 and 2

Compare electricity and gravity

Course Materials are always under revision! Weblecture content may change anytime prior to two weeks before scheduled chat session for content.

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Electrical Force

Lab: Electrical Force

Goal: To observe measure force due to electrical charge


  1. Balloons
  2. Scale
  3. Ruler
  4. Weights (uniform objects such as aspirin pills; coins are probably too heavy).
  5. Heavy duty thread.
  6. Container big enough to hold weights.(lightest possible plastic cup)
  7. Piece of silk, wool, or other fabric.


This lab is best carried out when humidity is low!

Data Handling

  1. Determine the gravitational force required to overcome the electrical attraction between the wall and the balloon. Fe = k q1 q2 r 2 = mg
  2. Assume that at the instant the balloon touches the wall, the induced charge in the wall attracting the balloon is equal to the charge on the balloon: q2 = q1. Using the radius of the balloon as r, calculate the values of q2 and q.
  3. Using the amount of charge per electron, estimate the number of excess electrons at the instant the balloon touches the wall.


  1. Describe your materials, equipment, and procedures in sufficient detail that your fellow students could repeat your experiment.
  2. Report your data. Be sure to indicate the amount of error in your measurements. For example, if you can only measure a mass of 25 gms within 1 gm, your error would be 25 ± 1, or 1/25 = 4%.
  3. Present your data in an organized form, preferably in a table, in such a way it is easy to compare results as you repeate trials or vary a specific contributing factor.
  4. Show a sample calculation, if you have calculated values.
  5. If you did a series of experiments, varying something by increasing or decreasing a factor, try to plot your data (y-axis) as a function of the factor (x-axis).
  6. You may use a spreadsheet to calculate your information and create your table.
  7. Summarize your results.
  8. Draw conclusions about what is happening.
  9. Suggest at least one way to improve your experiment.