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Soda Can Mirror

Science Snack
Soda Can Mirror
See how images appear in a curved mirror.
Soda Can Mirror
See how images appear in a curved mirror.

Wrap a piece of Mylar around a soda can to make a cylindrical mirror. Then create your own anamorphic art to explore how curved mirrors reflect images.

Tools and Materials
Assembly
  1. Make a cylindrical mirror (a mirror shaped like a cylinder) by wrapping the Mylar around the soda can. It should be loose enough so that it doesn’t reveal the wrinkles and imperfections in the can’s surface.
  2. Try to make the surface of the Mylar as smooth as possible, and then use tape to hold it in place.
To Do and Notice

Look at the distorted, or “morphed,” images you printed out. Can you tell what they are?

Place the Mylar-wrapped can in the circle next to one of the morphed images. Look at the reflection of the image in the curved mirror. What does it look like now? How has the mirror changed the image on the page? A mirror that distorts a reflected shape is called an anamorphic mirror.

Take your copy of the “Place Can Here” page and set the Mylar-wrapped can on the circle. Imagine that the line you see on each side of the can continues underneath it, forming the diameter of the cylinder (see image below).


Use the beans to make a series of points that connect this straight-line diameter in the reflection you see in the can.

To do this, place one bean in front of the can so you can see it in the mirror. Then, keeping your eye on the mirror, move the bean so its reflection lines up with the imaginary diameter line. Keep adding beans, one at a time, until you complete the extended length of the reflected line. The key is to keep looking in the mirror as you position each bean.

Once the reflection in the mirror looks like a straight line of beans, notice the shape formed by the actual beans on the paper (see photo below). How would you describe that shape?

Now take a look at the anamorphic grid you printed out: Some of those lines should look like your bean line. How do you think the grid’s reflection will look when you place the mirror in the circle? Try it and see what happens to the curved lines.

Remove the can and draw a simple shape on the grid of squares inside the circle. You might draw the first letter of your name, or some other simple design. Use your pencil to fill in each of the squares of your design.

Now you can change your design into anamorphic art! Just copy each shaded-in square in the circle to the corresponding “square” on the curved grid. Below is an example using the letter L.

Copy one square at a time. Count how many empty squares are between your original shape and the circle (which represents the surface of the mirror, or the origin of your reflection), and then start drawing your shape the same number of “squares” away on the outside of the circle (see photo below).

Keep counting and filling in squares as you map the complete reflection of your design onto the curved grid. When you’re finished, check your design by placing your mirror back on the circle (see photo below).

What's Going On?

Flat mirrors make normal reflections that maintain the length and width ratio of whatever object you put in front of them. But a cylindrical mirror, like the one you make here, creates a compressed reflection of the things around it.

If you draw a normal shape, it will look compressed in the curved mirror. But if you draw a stretched-out shape, its reflection will be compressed into a normal-looking shape. This kind of transformation of one shape into another shape is called anamorphosis, which means, literally, reshaping.

To create a compressed version of any design drawn in the circle on the anamorphic grid, that design must be reflected onto the grid outside the circle. When you put your curved mirror in place, the compressed design is not only reflected, but changed in scale as well. Squares farther from the surface of the mirror are more distorted than those that are closer. Compare the vertical scale of the squares inside and outside the circle. Compare the horizontal scale of the squares inside and outside the circle. While the squares are more spread out horizontally, the height of the squares—and thus, the height of the image—is conserved.

Going Further

Put your curved mirror on a clean piece of paper. Then, while looking in the mirror, try to draw what appears to be a straight line. What shape did you draw to make that reflection? Look in the mirror and try to draw what appears to be a curved line. What shape did you draw to make that reflection? Now, still looking in the mirror, try to write your name—and see what ends up on your paper.