Invisible Test Tube
Got yer attentin didn't it? Take a look at the photo above. It's of a test tube leaning in a beaker of cron oil. Note the tube is actually "invisible" in the oil! How come?
Well, here's whatcha do... Put any amount of corn oil, NOT regular veggie oil, in a beaker. Place a clean pyrex test tube into the beaker. You will notice the tube looks "bent" when viewed from the side of the beaker due to refraction of the light going thru the beaker, oil, and test tube. Common observation. Now, fill the test tube to the level of the corn oil in the beaker and VOILA! The bottom becomes invisible! It's actually kind of simple. The index of refraction of the pyrex tube is virtually the same as that of corn oil and they make the light bend by the same amount so there is no "boundary" between the tube and oil... Cool!
A follow up to the above demo is to take the two beakers and make one disappear! Place the baby beaker inside the big beaker. Pour oil into to smaller one and keep pouring even after overflow. The little guy inside will disappear! I usually draw a little face on the little guy with a wax pencil so the kids can see the 'floating' face inside the big beaker. Quite Kewl!
Here's an exciting little "magic" trick I like to do. Put a bunch of corn oil in a large beaker as shown. It has to be at least 3 inches deep. Now, after showing the test tube thing above, remove the test tube from the small beaker, wrap it in a towel, smash the poop out of it with a hammer right in front of the kids! Dump the totally obliterated shards of broken test tube into the larger beaker in plain sight of the kids. Now, while mumbling some meaningless mumbo-jumbo like, "sin i / sin r = c / v", reach into the large beaker, dig around a little and pull out a perfectly "put-back-together and repaired" test tube! (It was simply previously placed in the large beaker, but has remained invisible to the audience the whole time. There is one in the above picture! Try to pick it out. Go ahead, I'll wait...) It's absolutely amazing the reactions you get and it drives home the point of similar indexes - indices - indexii?!
CAUTION: Be very very careful with this one! Broken pyrex is sharp and will cut the dickens out of your fingertips if you aren't careful!
