Climbing Sphere Illusion

Mesmerize yourself and others with this amazing illusion. As the slinky twists and spins, it looks like the sphere climbs the spiral. But it doesn't actually climb - try it out to see how your eyes are tricking you!

  1. Ages: 5 - 16

  2. <30 minutes

  3. A little messy

Materials you'll need

Step-by-step tutorial

  • Step 1

    Gather your materials. Then, bend half of the first ring of the slinky up so that it forms the shape of a hook and tie one end of a piece of string to it.

    Photo reference of how to complete step 1

  • Step 2

    Tie the other end of the string to a tree branch.

    Photo reference of how to complete step 2

  • Step 3

    Push the ball into the twelfth ring of the slinky.

    Photo reference of how to complete step 3

  • Step 4

    Twist the string in one direction. Then, let go and observe what happens as the slinky spins in the opposite direction!

    Photo reference of how to complete step 4

  • Learn moreMagnifying graphic

    What’s going on here is an optical illusion. Optical illusions happen when your eyes and brain get confused by something you’re seeing, so the thing appears differently to you than it really is. And actually, there are two optical illusions at work here, so you’re doubly confused!

    The first illusion is called a Barber Pole Illusion. That’s what makes the slinky look like it’s moving up and down when it spins. Your eyes have trouble tracking the spinning motion, so instead, your brain is tricked into seeing the coils moving vertically. The same thing happens with a barbershop pole.

    The second illusion is called Induced Movement, and it’s why it looks like the sphere is moving. Because the slinky looks like it’s moving, your eye starts to follow that motion. Anything that doesn’t also move with that motion (like the sphere) appears to move in the other direction! Focus on the sphere, though, and the illusion will stop.

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