Educator How-To: The eyes have it in this DIY optical illusion

Your eyes are amazing sensory organs. They help you understand shape, color and form, judge distance and alert you to potential dangers. What you perceive as “seeing” is actually the result of a complex series of events that occur between your brain, your eyes and the world around you.

Light reflected from an object passes through the cornea of the eye and moves through the lens, which focuses it. The light then reaches the retina at the very back of the eye, where it meets a thin layer of color-sensitive cells called the rods and cones. Information from the retina travels from the eye to the brain via the optic nerve.

Because eyes see from slightly different positions, the brain must mix the two images it receives to get a complete picture. The light also crisscrosses while going through the cornea so the retina “sees” the image upside down. The brain then “reads” the image and turns it right-side up.

The rods and cones are what you call photoreceptors. When they are overworked, they lose sensitivity. Normally the small movements of your eyes that you make unconsciously, or regular blinking, will keep these photoreceptors sharp and happy. If you are looking at a large enough image, where your eyes can’t rest, or if you purposely hold your eyes still, you will tire out your poor rods and cones and they will adapt to this overstimulation by no longer responding. When you move your eyes to a blank space, your worn out photoreceptors create an “afterimage”.  An afterimage is where your eyes produce a ghost image, like when you stare at something a little too bright and you see dark spots in your field of vision. In an afterimage, light portions of the original image are replaced by dark portions and dark portions are replaced by light portions.

Try this out for yourself by doing the following activity. 

You will create the Texas state flag in some unusual colors. After you stare at this incorrectly colored flag and have worn out your photoreceptors, looking at a blank wall will create a ghost image of the Texas state flag in red, white and blue!

Activity:  Negative Afterimage

Materials:
Scissors
Glue
Paper
Green construction paper
Black construction paper
Yellow construction paper 

Ed How To Optical Flag 1

Procedure:

1. Cut your green and yellow papers in thirds, width-wise.

Ed How To Optical Flag 2

2. Cut a star out of the middle of your yellow piece.

Ed How To Optical Flag 3

3. Glue the yellow piece to one end of the black piece.
4. Turn the black paper so that your yellow piece is placed on the left.

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5. Glue the green piece to the bottom of the black piece.
6. Trim off any extra green.

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Now stare at the flag for a minute or so. Try not to have much in your peripheral vision so that you can concentrate on the flag.

Look away from the flag at a neutral colored wall or piece of paper.  You should be able to see the flag in red, white and blue!

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Have a school group and want to know more about how your eyes work?  Sign up for an Eyeball Dissection with our Labs on Demand.  These labs make a great addition to a field trip, but are also available to come to your school.

Interested in knowing more about how your body works?  Visit Body Carnival, a carnival-themed interactive exhibit that explores the connections between perception and the laws of physics in the human body, at HMNS Sugar Land. Enjoy learning about the human body while investigating force, pressure, light, and color. Crawl through a giant artery to see and hear the effects of restricted blood flow, test your balance in the 10-foot Dizzy Tunnel or don a pair of vision-distorting goggles and discover how sight affects your ability to walk straight. There’s a lot to explore!

 

Educator How-To: We’re batty for ornithopters

Bats have frightened, awed, and inspired for millennia. Leonardo da Vinci used the bat’s amazing wing structure as inspiration for his version of the ornithopter — a machine which flies using flapping bird-like wings. No one knows for sure if he ever built or tested his invention, but Cardanus, a contemporary of Leonardo wrote that he had tried, “in vain”, to get the orinthopter aloft.

A sketch of Da Vinci’s ornithopter

Here is a version of Leonardo’s creation that you can try your hand at constructing and flying. Our version is technically a glider, but looks much the same as Leonardo’s ornithopter design.

Materials:

  • Cardstock copy of orinthopter template
  • Large plain craft stick
  • Paper clips – large and regular size
  • Craft glue
  • Scissors
  • Scotch Tape ™
  • Markers
  • Thin hemp-type string
  • 18th inch hole-puncher
  • Bat specimen or pictures of bats
  • Picture of Leonardo’s orrnithopter

Building the Ornithopter:

  • Display the picture of Leonardo’s ornithopter and discuss how he came up with the design idea after spending a great deal of time observing birds.
  • Study the bat specimen and/or bat pictures. Compare and contrast the bat wings with the ornithopter wings: Are the wings more bird-like or bat-like?
  • Color a large craft stick using a brown marker.
  • Color the wings and tail on the orinthopter template and carefully cut out the pieces.
  • Give the wings shape by closing the small V-shaped notch on each wing so that both pieces touch and then securing on the underside with transparent tape.
  • Using craft glue, attach the wing and tail pieces to the craft stick as illustrated by the picture below. Allow time for the glue to dry.

Bat Orthinopter 2

  • Next, bend the wings up along the large V in the wing pattern and carefully crease.
  • Use a 1/8th inch hole-puncher to make small holes just to the inside where the wings were taped to give them shape.
  • Use a piece of thin string to create a loop through the holes with a loose knot to secure it in place. This serves to keep the wings from spreading too far and to adjust the wings up when tightened.

Bat Orthinopter 1

  • It’s time to test the ornithopter! Make different sized paper clips available. Use these to properly distribute the weight of the ornithopter for better flight.
  • Spend time re-engineering the after the primary test flight.

Educator How-To: Teaching tessellation, symmetry & point reflection

Tessellations — tiling a plane using geometric shapes without overlaps or gaps — are a pretty fun way to teach students about shapes, symmetry, reflection and rotation. Plus, they require the most minimal of supplies!

Materials:
•    Plain 3″ x 5″ index cards
•    Scissors
•    Scotch tape
•    Blank white paper
•    Optional: colored pencils/crayons, etc.

Procedure:
1.    Draw a simple design from one corner of the sheet to an adjacent corner. (Do not draw diagonally). Stress to the students that they must draw from corner to corner on this first attempt. Do not stop halfway across!

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2.    Cut on the design line, being sure to have two pieces when done. NO TRIMMING ALLOWED.

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3.    Slide the cut piece across the sheet to the opposite side and tape the straight edges together. The corners of the original card and the cut piece should match perfectly.

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4.    Repeat the procedure for one of the short side sides. Key points to remind students:

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  • Do not flip the cut pieces of your index cards
  • Do not overlap the edges of your cut pieces
  • Make sure you only cut one long side and one short side. The cut pieces will attach to the opposite straight edges
  • Cut exactly from corner to corner
  • When taping your cut piece to a straight edge, make sure everything lines up

5.    Once you have a completed pattern for your tessellation, place it anywhere on a piece of paper and trace around it. This example is squared up with the original index card edge and the paper’s edge, but this is not necessary.

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6.    Move your pattern so that its edges match up with the outline you drew. If done correctly, they should fit snugly together like a puzzle piece, leaving no gap. Trace around your pattern when it is in position.

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7.    Continue moving and tracing your pattern until your page is filled with your pattern’s outlines.

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8.    For extra fun, and in homage to M.C. Escher, you can add some details to your artwork!

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Background:
A tessellation is created when you cover a surface with a repeating pattern of shapes, making sure there are no gaps or overlapping pieces. The word “tessellation” comes from the Latin word “tessella.” Tessella were tiny squares of stone that were used to make large mosaics. The patterns for these mosaics were usually intricate and often geometric. This tradition continued in many different cultures, but is particularly well recognized in the Moorish artwork of Morocco and southern Spain. More recently, M.C. Escher applied the concept of tessellations to less geometric and more fantastical shapes. You may also recognize tessellations in nature in the form of bee hives, snake scales, and the outside of a pineapple.

Regular tessellations are made by repeating squares, hexagons and equilateral triangles – all regular polygons. If you figure out the interior angles of these three shapes, you might note something interesting…

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All of these numbers — 60, 90 and 120 — are evenly divisible into 360 degrees. This means that they fit together extremely well and make filling a space easy, either while touching themselves, as in triangle to triangle, or each other, as in triangle to hexagon. When you combine these three shapes to make a pattern, you are creating a semi-regular tessellations.

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When creating tessellations, it is important to understand reflection symmetry, rotational symmetry and point reflection.

Reflection symmetry occurs when you can easily divide an item into two and the two halves are identical. The dividing line is referred to as the line of symmetry.

With rotational symmetry, the polygon is rotated around a central point, without leaving the surface you are working on.

Point reflection occurs when you create a mirror image of a shape. Reflection is not terribly important if you are using the shapes in a regular tessellation as they are all perfectly symmetrical when divided in two. Reflection becomes much more important when you are using fluid shapes. This concept is important for students to understand as they make their tessellations. Their shapes won’t fit together correctly if they have been reflected!

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Educator How-To: The magic of magnetic fields

What better way to understand how magnetic fields work than to see them for yourselves?

Materials:
•    Magnetic field line cards (green) – one per child
•    Magnetic nail polish
•    Clear nail polish
•    Assorted magnets of various shapes and sizes
•    Large clear glass playing pieces
•    Button magnets (at least ½ inch)
•    E-6000 or other silicone glue

Procedure:
1. You will need to purchase some magnetic field viewer cards. They are sturdy and fairly inexpensive, so a single class set will last you a while. (You may also choose to just buy the magnetic film and make your own cards, but it doesn’t have the explanation printed on it.)

Educator How-To: Magnetic Field Magnets

2. Pass out a magnet and a magnetic field viewing card to your students. Try the magnets with the field line cards. What looks the same, what’s different? How do you think the field line cards work? [See the magnetic field viewer cards for more explanation.]

Educator How-To: Magnetic Field Magnets

3. Have the students trade their magnets around and see how the various shapes and sizes of the magnets affect the field viewer.

Educator How-To: Magnetic Field Magnets

4. Give each student a glass piece and place it on the table with the rounded side down.
5. Paint a thin coating of clear polish on the flat surface.

Educator How-To: Magnetic Field Magnets

6. Paint a reasonably thick coating of magnetic nail polish on the flat side of the piece. (Don’t shake your fingernail polish if it has been sitting on a shelf for a while. Instead roll it back and forth in the palm of your hands.)

Educator How-To: Magnetic Field Magnets

7. Quickly (there’s only a small window of time for this) use magnets to create a design now that you know what the magnetic fields will do to the nail polish! You want to put the glass playing piece and the magnets as close as possible without touching one to the other.

Educator How-To: Magnetic Field Magnets

8. Do not pick this up for a few minutes, and allow it to dry.
9. Once dry, use a silicone glue to attach a ceramic button magnet.

Educator How-To: Magnetic Field Magnets

10. Now use your magnets to hang up masterpieces, papers with no name and missing homework!

Educator How-To: Magnetic Field Magnets

How do magnets work?

Questions that often come up are, “How do magnets work?” or “Why is iron magnetic? or “What makes a magnet?” or “What is the magnetic field made of?”

Those are good questions, and they deserve a good answer. However, there is a lot about magnets at the atomic level that isn’t known yet. Just like with most of the other basic forces we are familiar with, such as gravity, electricity, mechanics and heat, scientists start by trying to understand how they work, what they do, whether there are any formulas that can be made to describe (and thus predict) their behavior so we can begin to control them, and so on.

The work always starts by simple observation (that’s the fancy word for playing around with the stuff!) That’s why it’s so important to have some hands-on experience with magnets.

Have your students take two magnets and tried to push like poles together. How far away do you start to feel the repulsion? How does the force vary with the distance between them? When the magnets are moved off-axis to each other (moving them to the side and not head on) what does it feel like? Could you describe it like trying to push two tennis balls together? When you flip one around, what changes? What about moving one around the other in a circle?

Encourage your students to try these things; that’s how you learn! Only when they play with magnets will they begin to understand how they work. This is the stuff great scientific pioneers did, like Faraday, Lenz, Gilbert, Henry and Fleming.

What we can find out through play are some of the basics of magnetism, like:

•    The north pole of the magnet points to the geomagnetic north pole located in Canada above the Arctic Circle.
•    North poles repel north poles
•    South poles repel south poles
•    North poles attract south poles
•    South poles attract north poles
•    The force of attraction or repulsion varies inversely with the distance squared
•    The strength of a magnet varies at different locations on the magnet
•    Magnets are strongest at their poles
•    Magnets strongly attract steel, iron, nickel, cobalt, gadolinium
•    Magnets slightly attract liquid oxygen and other materials
•    Magnets slightly repel water, carbon and boron