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Science 7–10 · Year 7

Static electricity: charging balloons and rods by rubbing

Physical sciences — Forces, content group Forces in action (NSW Stage 4 focus area; NSW teaches electrostatic forces in Stage 4, while ACARA has no Year 7 to 10 content description on static electricity, so only Year 7 inquiry codes are cited)

PracticalLow risk

The idea

Rubbing two insulating materials together transfers charge, and charged objects then exert non-contact forces of attraction or repulsion.

What you need

  • party balloons, 3
  • thread 50 cm, 2
  • polythene rod and perspex (acrylic) rod, 1 each
  • woollen cloth, 1
  • torn tissue paper pieces, a handful
  • tap with a thin stream of water
  • retort stand to hang balloons, 1

How to do it

  1. Before each step, predict whether the objects will attract, repel or do nothing, and write down the reason.
  2. Blow up two balloons and hang each from a thread on the stand, 5 cm apart. Rub both with the woollen cloth for 20 seconds and let them hang free; observe.
  3. Hold the woollen cloth near one charged balloon and observe; then hold a third, uncharged balloon near it and observe.
  4. Rub a polythene rod with wool and bring it near the tissue pieces without touching; observe. Repeat with the perspex rod.
  5. Hold a rubbed balloon 2 cm from a thin stream of tap water and observe the stream.
  6. Touch the rubbed balloon on a wall and time how long it stays. Repeat on a humid day if possible and compare.
  7. Record which pairs attract and which repel and explain each in terms of charge moved from one material to the other by rubbing.

What you should see

Two balloons rubbed with the same cloth swing apart, because both gain the same kind of charge and like charges repel. Each charged balloon swings toward the woollen cloth, which was left with the opposite charge, and it also swings toward the uncharged balloon, because a charged object attracts a neutral one; only repulsion shows that two objects carry the same kind of charge. Both rods lift tissue pieces before touching them, and the water stream bends toward the balloon. A charged balloon stays on a wall for longer on a dry day than on a humid one, because charge leaks away faster in humid air. The learner knows it worked when the two balloons repel each other while each is attracted to the cloth.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

  • Rubbing creates charge rather than moving it from one object to the other.
  • Charged objects only attract.
  • Static electricity is a different kind of electricity from current.

Safety card

Low riskLearners carry it out

Hazards

  • balloon bursting near eyes
  • latex allergy

Controls

  • do not over-inflate
  • offer non-latex balloons if needed

Note

No hazardous chemicals or naked flames are used. Complete the school's risk assessment for the activity before the lesson; the NSW Department of Education Science safety and compliance page points to CSIS 1.7 (Risk assessment – a pre-requisite for risk control) for how to carry it out.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Sources

The pages the author read to write this activity.

  1. curriculum.nsw.edu.au/learning-areas/science/science-7-10-2023/outcomes
  2. curriculum.nsw.edu.au/learning-areas/science/science-7-10-2023/content/stage-4/fa71c2a852
  3. spark.iop.org/forces-due-electric-charges
  4. spark.iop.org/introduction-electric-forces
  5. instructional-resources.physics.uiowa.edu/5a2020-electrostatics-pith-balls-balloons

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