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Friday
May292009

Communicating with Light

Connect an LED to the output of an audio source in such a way that the LED flashes with the source. Then attach an applified speaker to a solar cell and presto you are communicating via light.

<http://www.exploratorium.edu/square_wheels/modulated_led.pdf>

 

The Exploratorium has a series of books called "Snacks" which explain how to make cool science experiments. Unlike some other books, though, the experiments actually work, and also unlike other some other books their books come with correct explanations of the science behind them. Check out a selection at

http://www.exploratorium.edu/snacks/

You can find the books at most big public libraries. See a list at Amazon here.

Oh, full disclosure, I work/volunteer with the Exploratorium, but I've never worked on a Snack book.

Friday
May292009

Conducting Glass

Tap water conducts electricity, which seems kind of weird since water isn't a metal and has a covalent bond. Of course it conducts because it has ions dissolved in it that can move around and act like the electrons (in a way) as those in a wire. Pure water without ions is a lousy conductor.

Glass is the prototypical example of an insulator. It too is composed mostly of non-metals and has a covalent bond. And like tap water it too has ions. Why doesn't it conduct?

The ions are frozen in place, of course. Let's not argue whether or not room temperature glass is a solid -- suffice it to say that the particles aren't going anywhere fast. On the other hand, if you melt the glass, then the ions can move and then it will conduct electricity.

How to do this? Connect two lamp bases in series and then connect them to a wall plug protected by a GFCI. Carefully break the glass globe off a bulb. You will see a plug of glass with two wires coming out of it. The wires are in turn connected to the filament. Clip the wires to the plug of glass. Put an intact bulb in one socket and a the broken bulb in the other socket. Plug them into the wall. Careful, careful. You've got live current here. The GFCI will help but it's not perfect.

Take a torch and heat the glass plug until it glows red/orange. The other bulb will then light up. Notice that the plug will stay molten from the heat running through the wire. Unplug the apparatus. The bulb will go out and the molten glass will cool. If you plug it back in before the glass freezes, the bulb will light up again. If you unplug and wait until the glass is cooler (although still hot enough to burn you) before plugging it back in, then the bulb will not go back on.

Thursday
May282009

Solar Oven

According to solarcooking.org:

Solar cooking is the simplest, safest, most convenient way to cook food without consuming fuels or heating up the kitchen. Many people choose to solar cook for  these reasons. But for hundreds of millions of people around the world who cook over fires fueled by wood or dung, and who walk for miles to collect wood or spend much of their meager incomes on fuel, solar cooking is more than a choice — it is a blessing. For millions of people who lack access to safe drinking water and become sick or die each year from preventable waterborne illnesses, solar water pasteurization is a life-saving skill. The World Health Organization reports that in 23 countries 10% of deaths are due to just two environmental risk factors: unsafe water, including poor sanitation and hygiene; and indoor air pollution due to solid fuel use for cooking.

Plans <http://solarcooking.org/plans/> I like the solar funnel which is really easy to build.

My design is different than any of these and relies on the availabilty of satellite television dishes. In San Francisco, I often see Direct TV and Primestar parabolic dishes being thrown away -- not the receiver mind you -- just the metal dish. I then rubber cement aluminized mylar to the dish. These are amazing. They can get a pint of water to 160 degrees F in about 20 minutes and boil a like amount of water in about 30 minutes.

Wednesday
May272009

Electric Pickle

The electric pickle doesn't really show anything useful, but it's fun. The pickle always glows on only one side, but not always the same one. The glow is clearly from sodium ionization like a sodium lamp. Presumeably the current heats up the pickle and boils water away and at some point ionizes the sodium. It will go for some time but once you unplug the pickle it won't glow again.

This gives a starting explanation, and I always like a link to Hyperphysics <http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/pickle.html>

Some plans here.

 

 

Wednesday
May272009

Jumping Ring (Elihu Thomson Coil)

The plans to the right are from Brown University. Click to go there.

Jumping Ring video from MIT. Embedding disabled. More videos from Wake Forest.

.pdf plans from Sam Sampere are simplier to build.

 

Wednesday
May272009

Magnet Falling in a Copper Pipe

Not me in the video, by the way.

Eddy currents. The magnet falls far slower than you'd expect because it generates electricity in the pipe as it falls. That electricity then generates a magnetic field in opposition to the magnet's field slowing the fall. Coolmagnetman has a good site expaining what is happening and a couple of cool experiments to try with it.

Bill Beaty's (my hero!) has lots of cool stuff about rare earth magnets here including excellent plans and sources for pipe.

Tuesday
May192009

Vacuum Cannon

Vacuum Cannon

Lots of sites explain how to put them together. I like Sam Sampere's construction plan, but I use BYU's method of sealing the ends with Mylar.

This article from California State Chico does a great job of explaining the physics of the cannon.

More on figuring out the speed.

Tuesday
May192009

Singing Rod

The singing rod works via stick-slip forced vibration leading to resonance similar to a wine glass. However, the natural frequency of the rod is higher than the wine glass, so you need rosin to make your fingers more sticky rather than more slipprey like in a wine glass. This is rather more detailed than you will probably want.

One note, the first site at the Whelmers suggests that the singing rod is vibrating transversely. I'm pretty sure that's not the case. Put the end in water and you will see the water making concentric circles which looks quite a bit different than what a tuning fork looks like in water.

http://www.mcrel.org/whelmers/whelm10.asp
http://www.arborsci.com/detail.aspx?ID=491

Tuesday
May192009

Invisible Glass

Philosophical sounding question: How can you see somthing that is clear like water or glass? Reflections, yes, but more so, distortions of light coming through. The distortion is caused by light being bent when it changes index of refraction. This site will teach you how to mix up a solution with the same index of refraction as Pyrex. When submerged, the glass will be invisible.

http://gr5.org/index_of_refraction/babywess.jpg
http://www.exploratorium.edu/snacks/disappearing_glass_rods/index.html

Tuesday
May192009

Bed of Nails

Lots of good sources here. Start with this Australian site http://www.keypoint.com.au/~skeptics/Bed_of_Nails which does a good job of explaining how to make a bed, although I'd recommend going with galvanized or stainless steel nails even though they are harder to insert. Rust is a bad thing here.

This U. Pitt site gives a pretty good take as well. http://www.pitt.edu/~dwilley/Show/NailBed2.html.

If you have access to The Physics Teacher, there's a great article published in October 2004.

Another method with a video.

Tuesday
May192009

Bed of Broken Glass

The bed is 70 pounds of broken glass, mostly window panes. Yes, I walk on it barefoot. No, I haven't cut my feet yet. No, I don't have students do it.

I followed David Wiley's advice pretty much exactly. http://www.csicop.org/si/9911/willey.html

Who knew that everytime I was doing this activity I was deriving some valuable reflexology benefits? http://www.lifeevents.org/walking-barefoot-on-broken-glass.htm

Tuesday
Feb242009

Teaching Optics at Down to a Science

Down to a Science is a science cafe in San Francisco where the host Kishore plays a more active role than in most science cafes. In February 2009 he had a presentation on new directions in science education, and I was there to talk about high school science. He posted a video on YouTube. My part begins at about the 30 minute mark.

Click on the video to get a larger image.

Friday
Nov072008

Seed Magazine

Science Cafe in Sebastopol

Seed Magazine profiles science cafes around the country here. My gig in Sebastopol is mentioned on slide 12.

Thursday
Feb282008

Ask a Scientist

Being smashed with a sledgehamemr.Pictures are up from my February 2008 gig at Ask a Scientist! You can find them here about halfway down the page.

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