As you walk around your neighborhood, you probably see many other people, as well as some birds flying around, maybe some fish swimming down a local stream, and perhaps even a lizard darting behind a bush or a frog sitting contently on top of a pond. Most likely, you know that all of these living things are animals, but they are even more closely related than that.


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Tide pools are best observed undisturbed. But, they’re too shallow to snorkel… So how to can we explore them without removing their inhabitants? With an Aquascope! Aquascopes are very cheap and easy to make. With only a coffee can, some plastic food rap, and a couple of other items you can make a window into the world of tide-pools! In principle, aquascopes allow us to take a glass-bottom-boat tour of the rich ecosystems of tide pools. The plastic acts as the glass, while the coffee can allows us to break the distorting surface of the water.


Here’s a video to get you started:




Download Student Worksheet & Exercises


Here’s what you need:


  • milk or juice jug
  • plastic wrap
  • scissors
  • rubber band

Here’s the steps to make the waterscope:


  1. Clean out your jug first. Then cut the bottom and top off without cutting off the handle.
  2. Cover the opening at the bottom with your plastic wrap, securing it in place with the rubber band. Use tape if you need extra support to hold the plastic wrap in place. The window needs to be water-tight.
  3. Place the waterscope in the water, bottom-side down. You’ll be able to see all kinds of interesting creatures through your scope!
  4. Try to keep your scope still so the animals won’t be afraid to come close to you so you can have a good peek at their world.   The aquascope works the same way snorkel goggles work—except you don’t have to get wet!

Why this works: You can’t see clearly underwater with just your eyes for a couple of reasons. One is the thickness of the lens on your eye, but the main one is the index of refraction of water is different than that of air. Light rays bend when they travel from one medium to another of different density (refer to the Disappearing Beaker experiment for more on this topic). The amount that the light bends depends on refractive index of each substance along with the shape. The eye focuses images on the retina, and our eyes are built for viewing in air. Water has approximately the same refractive index as the cornea which effectively eliminating the cornea’s focusing properties. This is why you see a blurred image underwater. The eyes are focusing the image them far behind the retina instead of on the retina. The waterscope puts a layer of air between your eyes and the water (the same way goggles do) so you can view underwater without blurred vision.


Troubleshooting: The key to the aquascope is the taught plastic wrap. If it’s loose, or if there are holes, it won’t work as well. Make sure that the plastic wrap is securely fastened to the can, and is stretched tight. If you find your waterscope leaks, use a stronger rubber band to secure your plastic wrap in place. You can alternatively use strong waterproof tape or hot glue to secure it in place, but use the rubber band first so you can stretch the film tightly over the open end.


Exercises


  1. What is the term for light rays bending?
  2. Why is underwater vision blurred?
  3. How can we focus vision underwater?

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