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Saturday Science: The Reversing Arrow

Saturday Science: The Reversing Arrow

It's like magic...but it's science! In this Saturday Science from Play-Based Learning discover how you can change the direction of an arrow with only a glass of water. 


  • Glass of water
  • Pen
  • Paper
  • Spoon


  1. Draw an arrow on a piece of paper.
  2. Place it behind an empty glass, pointing to the right.
  3. Fill the glass with water.
  4. Experiment with other glasses to find the ideal shape for the experiment.
  5. Continue to check the arrow to see if it's pointing in the opposite direction.
  6. Try writing letters and other shapes on a piece of paper. Does it still work?


The idea of this experiment is to show how the refraction of light through water changes things. It is an optical illusion, called refraction.  Light only bends when it passes from a substance of one density into a substance of a different density—in this case from air to water.

Next, trying seeing how the concave (turning inwards) surface of a spoon reflects the image upside down. This happens because, being a concave surface, the light waves hit the different parts of the spoon at different angles, so they’re all bent a little bit differently. By the time they come back to you, they’ve all bent differently in such a way that they end up making things look upside down.

Want more Saturday Science? See all of our at-home activities on the blog or on Pinterest