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Flying Optical Illusion

You can perform a number of optical illusions using mirrors. 

This illusion works because our eyes and brains tell us that the reflection of the leg in front of the mirror is actually the leg behind the mirror. 

Suppose you have your right leg in front of the mirror. In the mirror, the students see the inside of your right leg facing them, in the exact orientation they’d expect to see your left leg. 

The light bouncing off the mirror acts as though it comes from a leg behind the mirror, in the exact location where we would expect to see a left leg.

When you lift the leg in front of the mirror, the reflected leg also lifts. The illusion is that both feet have lifted from the ground!

This demonstration is so good you will think you are flying! 

Objectives

  • Explain properties of visible light.

  • Describe how light rays can change direction.

  • Demonstrate how visible light is reflected.

Materials

  • large flat mirror

Key Questions

  • How many legs are you actually seeing?
  • Which part of what legs are you seeing?
  • Why is our brain tricked in this way?

What To Do

  1. Stand at the front of the class where all the students can see. Stand the mirror up on the floor (you may need a pair of volunteers to hold it up vertically.
  2. Straddle the mirror with one foot in front of the mirror and one behind the mirror (out of sight of the class).
  3. Lift the foot in front of the mirror. Both legs will appear to leave the ground, and it will look like you are flying!
  4. Ask the students to explain how the illusion works.

Extensions

  • Invite student volunteers up for a “flight.” Can students think of other illusions they can create using a mirror?