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Activity: Electrostatic Forces

NGSS Science and Engineering Practices:

NGSS Crosscutting Concepts:

NGSS Disciplinary Core Ideas:

Materials

  • Hard-rubber comb
  • Glass rod
  • Piece of silk or nylon
  • Two pieces of polystyrene foam
  • Two pieces of string or thread
  • Ring stand and ring
  • Aluminum foil
  • Paper
  • Towel

 

Procedure

Safety Note: Electrostatic forces are very sensitive to the environment. As you conduct this activity, be careful not to get fingerprints on the materials. Do not allow the materials to touch your clothing. Make sure classroom windows are closed. Because humidity greatly affects electrostatic forces, conduct the activity in an air-conditioned room. Do not conduct this activity on a metal table. You may have to repeat each step several times, taking these precautions each time.

  1. Clean the hard-rubber comb and glass rob. Remove all of the water with a towel.
     
  2. Tear up the paper into tiny pieces. Make a small pile of the pieces of paper.
    1. Produce a negative (–) charge on the comb by rapidly passing it through dry, greaseless hair (straight hair works best). Bring the charged comb near the pile. Record what you observe.
    2. Produce a positive (+) charge on a glass rod by rapidly rubbing it with silk or nylon. Bring the charged rod near the pile. Record what you observe.
       
  3. Set up the ring stand and hanging objects.
    1. Attach the ring stand and ring.
    2. Tie one of the pieces of polystyrene foam to a piece of string. Tie a small strip of aluminum foil to the other piece of string.
    3. Tie the strings to opposite sides of the ring. The objects should hang at the same height.
       
  4. Observe how negatively charged objects interact. Record all of your observations.
    1. Charge the comb (–) and bring it near the polystyrene foam piece.
    2. Charge the comb (–) and bring it near the foil piece. 
    3. Give both the polystyrene foam and the foil a negative (–) charge with the comb by touching them with a charged (–) comb.
      1. Re-charge the comb (–) and again bring it near the polystyrene foam and the foil. 
      2. Bring the charged polystyrene foam and foil as close as you can without touching. 
    4. Discharge the polystyrene foam and foil by touching them with your hand.
       
  5. Observe how positively charged objects interact. Record all of your observations.
    1. Charge the glass rod (+).
    2. Repeat procedures 3 c and d with the charged glass rod.
       
  6. Observe how different positively and negatively charged objects interact. Record all of your observations.
    1. Give the foil a negative (–) charge with the comb and the polystyrene foam a positive (+) charge with the glass rod.
    2. Bring the polystyrene foam and foil as close together as you can without touching.
       
  7. Observe how objects that are the same except for their charge interact. Record all of your observations.
    1. Replace the foil with a second piece of polystyrene foam.
    2. Give one of the polystyrene foam pieces a negative (–) charge with the comb and the second a positive (+) charge with the glass rod.
    3. Bring the two polystyrene foam pieces as close together as you can without touching.
Activity Questions: 
  1. How did your group’s results compare with the results of other groups in your class?
     
  2. What charge, if any, was on the polystyrene foam, the foil, and the tiny pieces of paper before electrical charges were brought near them? What is the reasoning for your answer?
     
  3. What charge, if any, was on the polystyrene foam and the foil after the electrical charges touched them? What is the reasoning for your answer?
     
  4. Describe the interaction between each pair of materials you used. Use the terms attract, repel, and no attraction.
     
  5. If your materials did not react as predicted, why do you think this may be?  What could you do differently?
     
  6. Describe the interaction of
    1. like charges
    2. unlike charges

Table of Contents:

Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.