Ask Mr. Science
page 35

 
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ants biting
Why do ant bites hurt?
and other animal defense strategies

escape
camouflage
playing dead  (possums, snakes)
trickery, mimicry
physical : quills, shell
chemical (skunks, stinkbugs, bobardier beetles...)

 some unusual defenses

...some more



February 2020
 

Sending information

I always stert with a bit of history:

Way back, the fastest way to send messages was by carrying them by a courier on horseback.

In the late 1700's in France...

High-speed communication

Telegraph Samuel Morse 1838

Morse code generator

Telegraph Samuel Morse 1838

Via radio waves: 1890's James Clark Maxwell, Heinrich Hertz, Nicola Tesla, Guglielmo Marconi

Alexander Graham Bell patents the telephone 1876

1915 coast-to-coast call

digital data over the phone line

Telephone modem

Radio & wire: frequency, wavelength, line-of-sight, analog/digital

analog-to-digital

To show how this works, I used a prism and a laser pointer to show the transition between refraction and tota internal reflection as you change the angle of the beam.

Total internal reflection is of course how optical fibers work. I have some broken fibers. Removing protective layers, you can see the glass fiber itself, which is about the thickness of a human hair.

I also have some 1-mm plastic wavelength-shifting fibers. They are bigger than the glass optical fibers, and they also light up along the length. In addition, they light up green even if you use the purple laser. But that's a whole nother story.


Bring:
  • Fixture + bucket
  • Laser pointers (with spare batteries)
  • Towel
  • Funnel
  • Optical fibers
  • Wavelength-shifting fibers
  • 3L bottle with water
  • Container with a little bit of milk
  • Clear rectangular container
  • Prism (in cardboard holder)
  • Tape
 
The fixture

Why make a fixture? I have one hour in the classroom, and no advance setup time. I have a small table to work on. This fixture holds all the bits firmly in place, and everything is easily adjustable, so no time is lost. The base plate has a holder for the bottle, rolled from cardboard. A block with notches for rubber bands is attached. The clothespin functions as the switch for the laser. Note I glued a piece of a straw into the bottle, instead of just making a hole. This ensures that the stream of water is (initially) very smooth. The cardboard box that holds everything serves as a raised platform. Since everything gets wet, the fixture gets a coat of paint, and I put some plastic shelf paper on the box.


March 2022
 

ants biting
Simple electrical circuits
with copper tape and an LED

xxx

Copper tape circuits


Sep 2022





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