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Attractive Balloons

Positive and negative charges are opposite and attract, but how does a neutral material react around something charged?

In this activity, students will observe the effects of charged objects on neutral materials. 

The negatively charged balloon (from rubbing against hair) will repel the electrons of paper/water/aluminum cans away from the spot closest to the balloon, resulting in a positive charge on the paper/water/aluminum can. The negatively charged balloon then attracts the induced positive charge on the neutral material. The result is that the balloon can pick up the paper, deviate the stream of water, or attract the can.

Objectives

  • Explain how static charge causes materials to attract or repel each other.

Materials

  • Per Class:
    a sink with a tap

  • Per student:
    a balloon (and a few extra)
    a handful of confetti from a hole puncher, or small torn up scraps of paper
    a triboelectric series table

  • Per group of 3-4 students:
    a pop can
    a measuring tape (optional)

Key Questions

  • What happens to the confetti when you hold a charged balloon near it? Why?
  • What happens to the stream of water when you move the charged balloon near it? Why?
  • What happens if you let the balloon touch the water?
  • Can you get the can to move? How about tip over? Hint: try moving the can when it is on its side?

What To Do

Part 1: Picking things up

  1. Explore the most effective way of charging your balloon (e.g. rubbing it against your head, clothing, or other material).
  2. Slowly bring your charged balloon close to the confetti.
  3. Record your results.
  4. What other items around the classroom can you attract (pick up)?

Part 2: Moving a stream of water

  1. Turn on the tap so that you have a slow, solid, steady stream of water. Take turns slowly moving a charged balloon towards the water and observe. Be careful not to touch the water.

Part 3: Challenge: How far can you move a pop can with a charged balloon?

  1. With your team, work together to try and move the pop can using only charged balloons (no touching the can with the balloons!).
  2. Roll out a measuring tape on the floor. How far can you get your can to move before the balloon loses its charge?

Extensions

  • Do you push or pull the can with the balloon? Why? Use the triboelectric series table to deduce the movement of electrons between your hair and the balloon, then between the balloon and the can. Draw a picture showing the relative location of the electrons on each.
  • Hand out a mixed pile of salt and pepper and challenge students to separate the two. Salt is heavier than pepper, so holding a charged balloon over the pile will result in the pepper flying up and sticking to the balloon. If you move closer to the pile, the salt will eventually fly up too, so move slowly to get the best separation!
  • Extend the water activity by investigating more variables. Does the temperature of the water affect how much it bends? Does a bigger balloon make the water bend more? How does the strength of the stream flow affect how much it bends?
  • Create a mini race between two groups by challenging them to move their pop can from a starting line to a finish line first. The distance to travel should be about 30 cm i.e. enough distance that the can will require several “pushes” from the balloons in order to roll the whole way.
  • Run the "Balloon and Static Electricity" simulation from Boulder's Physics Education Technology at the University of Colorado. Students rub a balloon against a sweater and visualize the movement of electrons as they bring the charged balloon to a neutral wall.