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STEM Activities

Build an Ion Wind Rotor

Summary

Active Time
20-30 minutes
Total Project Time
20-30 minutes
Key Concepts
Electric charge, forces
Credits
Ben Finio, PhD, Science Buddies
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https://www.youtube.com/watch?v=SYJP36RJKPA

Introduction

Can you use electrically charged "wind" to make something move? Find out in this fun project as you build your own ion wind rotor.

This activity is not recommended for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

Materials

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Prep Work

  1. Make sure you read the instructions for the Van de Graaff generator and follow all safety measures when operating it.
  2. If you are using an aluminum beverage can, have an adult help you cut a flat piece from the side. Be careful because this can result in sharp edges.

Instructions

  1. Use the ruler and marker to draw an outline for your rotor on the piece of aluminum. The exact size and shape of the rotor does not matter as long as it is symmetric. It should be long and skinny with two triangular tips pointing in opposite directions at each end. Make sure the back edges of the rotor blades (opposite the tips) are rounded, not pointed. Carefully mark the exact center of the rotor.
    2D outline of an ion wind rotor showing the pointed tips and a cross marking the center Image Credit: Ben Finio, Science Buddies / Science Buddies
  2. Use scissors to carefully cut out the rotor.
  3. Use the larger nail to punch a hole exactly in the center of the rotor. If you find this to be difficult, place a piece of scrap cardboard behind the rotor as you punch the nail through.
    Ion wind rotor cut from aluminum, with a hole punched in the center Image Credit: Ben Finio, Science Buddies / Science Buddies
  4. Flip the rotor over, and use the head of the nail to flatten any sharp edges that may be poking out around the hole.
  5. Cut two small pieces of electrical tape.
  6. Punch the small nail through the center of one piece of tape with the sticky side facing toward the head of the nail. Slide the piece of tape all the way down to the head of the nail.
  7. Wrap the other piece of tape several times around the base of the nail.
    A nail standing vertically on its head, with one flat piece of electrical tape at the bottom and another piece wrapped around the base Image Credit: Ben Finio, Science Buddies / Science Buddies
  8. Slide the rotor onto the nail.
  9. Press the pencil eraser onto the top of the nail. This will keep the rotor from flying off.
    Aluminum rotor on nail shaft with pencil eraser on top Image Credit: Ben Finio, Science Buddies / Science Buddies
  10. Make sure the rotor can spin freely without getting stuck. If it gets stuck, remove the rotor and use the larger nail to widen the hole and flatten any rough edges. Repeat this process until the rotor can spin freely on the smaller nail.
  11. Tape the nail vertically to the top of the Van de Graaff generator. Make sure to press down firmly, so the nail is in electrical contact with the dome.
    An aluminum propellor with pointed tips, mounted on a nail that is taped to top of Van de Graaff generator Image Credit: Ben Finio, Science Buddies / Science Buddies
    Think about:
    What do you think will happen when you turn the Van de Graaff generator on?
  12. Turn the Van de Graaff generator on and watch your rotor closely. Was your prediction correct?

Cleanup

  1. Follow the instructions to safely turn off your Van de Graaff generator.

What Happened?

When you turn your Van de Graaf generator on, your ion wind rotor should spin like a propeller! If it gets stuck and does not spin, there might be too much friction between the rotor and the nail. Remove the rotor and try widening the hole. If your rotor is not symmetric, it may tilt at an angle and get stuck on the nail. If you cannot repair the rotor (for example, by trimming excess material from one side), try making a new one and make sure you measure carefully. Read the Digging Deeper section to learn how your ion wind rotor works.

Digging Deeper

A Van de Graaff generator builds up static electrical charge. It accumulates excess positive charges on the dome, which can result in a shock when you touch it! Since your rotor is connected to the dome via an electrically conductive nail, it also accumulates positive charge. However, these charges are not evenly distributed. They cluster near sharp corners, like the pointed tips of the rotor blades. This concentration of positive charge causes electrons to be stripped from nearby air molecules, turning them into positively-charged ions. The now positively-charged ions are then repelled from the positively-charged rotor tip, pushing them away. According to Newton's third law of motion, for every reaction there is an equal and opposite reaction, so the air molecules also push back on the rotor. This causes the rotor to spin.

Diagram of the ion wind rotor in motion with multiple small crosses indicating positive charge accumulating at the pointed tips, arrows indicating the direction of force from nearby air molecules against the pointed tips, and arching arrows indicating the direction of spin. Image Credit: Ben Finio, Science Buddies / Science Buddies

Ion thrusters, also called ion drives or ion engines, are used in real spacecraft to propel them through space. These thrusters do not spin like your rotor, because they all point in the same direction. They propel ions in a straight line out the back of the spacecraft, pushing the spacecraft forward.

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For Further Exploration

  • What happens if you try this experiment with a rectangular rotor that does not have pointed tips?

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