Upcoming Shows!

I have three upcoming shows as part of the Bay Area Science Festival. Friday is a small intimate show at the Atlas Cafe from 6-7 http://www.bayareascience.org/11/04/science-pub-crawl/. On Sunday (tentatively at 2 pm), I'll be at AT&T Park for Discovery Days http://www.bayareascience.org/11/06/dd-at-att-park/ but first, I'll be at Mad Scientist Nightlife at the California Academy http://www.bayareascience.org/11/03/mad-science-nightlife/.

Magnetic Clamp

A few companies sell a magnetic clamp for creating strong magnetic fields. Although the clamps are sturdy and versitile, they are expensive. Often very expensive. I decided to make my own.

I used a Jorgensen wood clamp. The clamps are very strong, and the threaded screw rods allow for very precise adjustment. The magnets are from K&J Magnetics and are 1" x 2" x 0.5" N42 rare earth magnet with (and this is the good thing) counter sunk screws holes. Excellent. Mine took a #10 screw and I used non-magnetic stainless steel, though magnetic steel would have probably been okay. (They are out of stock on this particular magnet, but they expect more and others would work.) 

The key is to drill holes in the wooden handle first, then drive in the screws. 

The idea was to make a pendulum that would show eddy currents. The bar is made of aluminum an 1/8 inch thick and the plates are made from 6 x 12 x 1/8 inch aluminum as well. I cut the slots on a miter saw but I don't recommend that as it was very dangerous, although it works with a carbide blade. I tried a bunch of ways of attaching the plate to the blade, but opted for the clamp which can be changed out the quickest. All the metal was obtained from Online Metals. They cut to order and for cheap.

Resonance Glass Breaker

Breaks glass with sound. If you look carefully you can see a broken piece of glass.I built a copy of David Kardelis's glass breaker. <http://www.personal.psu.edu/ref7/apparatus/2006%20competition/kardelis.htm> It breaks pieces of window glass rather than wine glasses. It has some cool advantages over the traditional wine glass breaking with sound. 

• The neatest thing is that it debunks the idea that only crystal wine glasses can be shattered with sound. 
• You can see from a distance that the glass is moving and the mode of vibration is really obvious.
• The breaking frequency is about 34 Hz, nearly outside the range of human hearing. Much more comfortable. 

The glass breaker has three holes. Two supports are added and a strip of window glass is placed on top them.  Sound waves come out of the holes, with the two outside holes being totally out of phase with the center hole. The sound is generated by two speakers that face each other inside of the box.

The inside of David Kardelis's box. I forgot to take a picture before I sealed mine up.

I broke 3 inch by 24 inch strips of window glass at 33.5 Hz.

I've made a few changes to make glass breaking more reliable. 

First, used window is full of micro-fine cracks almost invisible in the glass. These make the glass easy to break. New window glass is much, much harder to break and when it breaks it makes many small pieces. So, when I use new glass, I score it with a glass cutter around the center to help control the breaking.

Second, I bought a good subwoofer amplifier that cost about $100. Mine is a 12 V car amplifier that I run with a computer power supply. You could buy a plate amplifier too. The advantage over a normal receiver is that the output current and voltage have much lower distortion. Subwoofer amps also dissipate heat better. I have burned out a receiver running it for a long time. 

Third, after some excellent advice from fellow physics demonstrators on the mailing list TAP-L, I bought an HP 204C frequency generator. It makes beautiful sine waves. Other frequency generators, especially digital ones, often produce sine waves with jaggeties that seem to interfere with motion. Many of the them make obvious high frequency sound. A picture from HP MemoryI bought mine on Ebay for a good price of about $50. 

With these changes, it breaks glass more reliably than my wine glass breaker without blowing my eardrums out. 

Optical Illusion

Optical illusions sometimes seem like artifacts of the graphics and drawing, but sometimes normal objects can seem strange. Look at the bicycle gears and hub below.

(Click to enlarge.) Weirdly, they don't look like they both will fit on the same hub. To my eyes, the center hole of the left gear set looks smaller than the center hole of the right gear.

They are of course the same size.

 

And they both fit on the hub.

This is a physical example of a classic optical illusion where the size of the outside affects your opinion of the inside. The Exploratorium has a good Adobe Shockwave implementation of this effect. <http://www.exploratorium.edu/exhibits/changingill/> The third illusion is pretty much the same as this one.

What suprised me was that the illusion was just as strong in person with real objects as with a graphic on a screen.

Weird Shadows

My school has window with our school name on it in vinyl letters.

In the morning on a sunny day, they cast a shadow on the wall.

The picture is actually in focus, but the shadow is blurry. Notice something interesting about the shadow. The places where there are holes, like the center of the "o" in community or the "B" in bay are actually darker than the shadows of the letters. Weird.

If you put a piece of posterboard closer to the glass, the centers are brighter like you'd expect. 

As the board gets farther from the window the holes close up and then get darker.

Seeing Where the Microwaves Are

Microwaves are invisible, so you can't see them inside microwave oven, but their presence can be detected with neon lamps. The changing electromagnetic field from the microwaves will make charged particles move, and so the electrons in the metal legs will move creating current. This current makes the lamps glow. I drilled a grid in a piece of 1/4 inch acrylic and slipped the lamps in. I bought the lamps here, but Tom Senior found a better price here. As the platter turns, the lamps light up showing where the microwaves are the strongest.

My grid is based on another group's work.

Vortex Launcher

Steve Spangler Science http://www.stevespanglerscience.com/experiment/00000076 gives a pretty good description on how to make a Vortex Launcher.

Just after Halloween is the time to buy a fog machine. They get very hard to find by spring and you will need to pay a fair bit more to buy one.

Smaller vortex launchers like the Zero Launcher are pretty cool too. http://www.amazon.com/Zero-Toys-Launcher-BLUE/dp/B000FK5JR4

Cracking off Bottles Into Cups

I've had pretty good luck making glass cups out of bottles through this method. While the break is rarely perfectly straight, it is usually good enough to make a glass out of it. 

The comments from the Corning Glass Museum point out that a fine flame works better, and I've used both kinds of torches. The fine flame does seem a bit better, but a plumbers torch works too.

If the bottle has lots of bumps in it and looks irregular, it will probably cut weirdly.

Make your scribe mark straight. The crack seems to follow its directions, so if you scribe at an angle, cut will be at an angle.

I haven't used Dan Rojas's technique since I haven't bought the equipment. His solar oven materials are excellent, so maybe this is a better method too.

Cup Speaker

There are lots of designs of this, especially ones that use paper plates and suspensions. They all seem much more complicated and finicky for barely any more sound. This http://www.exo.net/~pauld/activities/magnetism/speaker.html from Paul Doherty of the Exploratorium seems to work the best, especially for the novice.

Melting Glass in Your Microwave

My hero Bill Beatty shows how to do this on Vimeo. http://www.metacafe.com/watch/1004040/melt_a_frickn_beer_bottle/ The process is relatively straightforward. Remove the glass plate and rotator from your microwave. Place an empty label-less bottle toward the back of a microwave. Warm the side facing you with a propane or MAPP gas torch, then hone in on an individual spot until it glows red. Close the door and start the microwave.

Mini-Marshmallow PVC Blowgun

Hovercraft Video

Videos

I've uploaded several more videos.

Breaking the bottom out of a bottle

Walking on Broken Glass Video

I'm starting to upload the videos that Betsy Baum (thanks!) took of me at the Maker Faire. First up, walking barefoot on broken glass.

Walking Barefoot on Broken Glass. from Marc "Zeke" Kossover on Vimeo.

Blue Ribbon!

I won an Editor's Choice Award for my physics presentation at the Maker Faire! Woo hoo!

Hovercraft

The easist solution is to buy the full thing from Pasco, but at $319 it is expensive. A kit that includes everything but the board and air supply is cheaper at $139 but is still costly but not outrageous, especially if you already own a cordless leaf blower. I really recommend this kit.

Building your own is pretty cool too. This set of plans from Bill Beatty (my hero) explains what to do really well and will set you back less than $50 plus the cordless leaf blower.

However, you can combine both of these sets to get a great design for a bit less money. Make the skirt in Bill's plans by using ballistic nylon like Pasco uses. Buy a yard and a half of 330 or 500 denier cordura nylon, like this stuff. Cut it into a circle a couple of inches larger than your hovercraft disk. Hem a hollow edge all the way around the outside of the circle. Follow Bill's advice for cutting circles out of the center. Thread a piece of stiff wire around the seam. By pulling the wire tight, you can keep the skirt attached to the board.

You will need to seal the skirt along the edge. Staples and silicone sealant will probably work, but heavy staples and heavy tape work well too. A rubber bumper like the one Pasco sells used to be available online, but the company where I saw it has gone out of business. (Thanks Steve for telling me!) I'm looking for a replacement.

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.

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.

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.

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.