A Radiometer

Joke: How did the bull feel in the milking shed? Udderly useless!

Try this:

  1. Seal the small end of an eyedropper in a flame. After it cools, cut one inch off the end with a file.
  2. Punch a hole in the centre of a 2 inch square piece of light card so it fits snugly over the tip of the eye dropper.
  3. Remove the cardboard and make cuts shown by the solid lines.
  4. Bend the card down along the dotted lines to form vanes.
  5. Blacken the side of each vane by holding the card carefully over a candle.Mark one side with an "X"
  6. Stick the large end of a needle into a cork and place the cork in the glass jar.
  7. Set the eyedropper tip and cardboard vanes over the needle.
  8. Fasten the lid and try to remove as much air as possible witha vacuum pump.

Since most of the air has been removed from inside the radiometer, the paddle wheel or vanes are free to move. Normally the vanes would strike air molecules and be slowed or stopped. With the air removed, the slightest sunlight energy striking the vanes will start the paddle truning.


  1. Is there wind in space? If not, what is the Solar Wind?
  2. How do solar panels work?
  3. What is the difference between renewable and non-renewable energy? Give some examples of each type.

RETURN TO FUN! Science Activities and Technology Projects


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