Lecture Demonstrations on video

I started to write indemoveritas because the available, official, tools were not so good.   There was no way to just throw some pictures up, or post a video, on our demonstration site. Over the past couple of years, that has changed.   The site is much easier to edit.  I’m even looking forward to writing up my chemistry demonstrations, which hitherto were just references to the literature.

Still, when we have a video, there is nothing like youtube to put that video out in the world.  So we made ourselves a youtube channel, NatSciDemos.  Wicked fun, and has given us a renewed excitement about Friday afternoon hacking sessions.

Of course, since we are all facebook users, it made sense that there should be a NatSciDemos on facebook, which of course, now there is.  It makes for easier sharing of videos to friends and friends of friends, etc.

Our most viewed video is called Pendulum Waves.  Very pretty and relaxing, it has been featured on a number of video-of-the-day sites, which, if I were a good blogger, I would have a list of here.  Ach, well.   I’ll get to it.

I am currently getting registered to go to the ACS national meeting in Denver, for three days of networking and learning.  I plan on taking a short course called Food Chemistry for the Non-Food Chemist.  I am the demonstrator for SPU27 Science of Food and Cooking, so it’s right up my alley.   I have no idea if any chemists read this, but if you are going to be in Denver, email me.  I will be leaving the meeting on Tuesday, because classes start for me on Wednesday.

So just a quick post to connect some of my recent work to indemoveritas.  Good surfing.

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From the depths of Widener Library

With a folded slip of paper in hand, I descended to the lowest level of the library.  Cold marble underfoot, the smell of a million books in my nose, I searched for WID-LC  PG7158.L392 A35 1997.

Books on the theory of teaching university level…what now?  Oh, I see, I am in WID-LC LC####, silly mistake.  Just run up a couple levels and head from East to West, wait, there is no connection on B-level.  So up another couple levels and here I am again at the entrance to the stacks, a quick reboot.

East to West, down two, and now I am in the 20th century Polish author section, picking out A Stanislaw Lem Reader.  Oh, and what else do we have here?  English translations only cover about half his ouvre and I don’t want to grab too many books, so just One Human Minute and Cyberiad for now.  I’ll be back.

Oh wait, check out Peace on Earth.   When I got it out of the library years ago, there was a printing error and about 25 pages after pg. 110 were doubled, with 25 pages missing.  An ugly rebinding at least has made the book whole.  I had to buy the book to finish it, and like all my other Lem purchases, it disappeared into the collection of whomever I lent it to.

Which reminds me of an old joke.  A Texan new to the college asks an ascot wearing preppy, “Where’s the Widener library at?”  The preppy responds cooly, “At Harvard, we don’t end our sentences in a preposition.”  To which the Texan responds, ” Well, then, where’s the Widener library at, asshole?”

So I done reboot my indemoveritas blog, and I “lost” all of the subscribers, some of whom were real, and many of whom were spam-bots and worse.  Best regards to the humans. –D

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Newton’s Cradle: Fail!

Our lecture demo of Newton’s Cradle, also known as Collision Balls, dropped one of its steel balls.   Fortunately, it is one of the outer balls, which means we can still use it, but with only five balls.  The wikipedia page linked above has our actual apparatus as the first reference.

The balls are 1  7/16″ in diameter, pretty random size, but dictated by the spacing of the holes for the suspension threads.  Each ball is suspended by two threads, on either side.  The technical term is bifilar suspension, which reduces the degrees of freedom of the ball. The thread goes into the frame, and is taken up on a tapered peg.  Just like a tuning peg, it allows for adjusting the two strings to the same length.

The balls are held to the thread with a blob of epoxy.  Weak.  Which is why it failed.  The epoxy can pop off of the ball bearing with the string still embedded in it.  That is an easy fix: roughen the ball with sand paper and epoxy the blob of epoxy back on.  The string can also pull out of the epoxy.  This is a different problem, with a more sharply applied force, and not as amenable to a crufty fix.

So I’m all like, let’s just replace the balls with chrome steel balls that have tabs welded to the top, like little loop ears, so we can tie the string to the loops and get suspended that way.  So out onto the inter-tubes I go, my search engine chugging away, and nothing like that exists (within my search parameter space.)   Wha…?

The current plan is to buy a dozen chrome steel balls, of one and seven sixteenths of an inch diameter, find a spot welder, and make our own.   The demo site will have details when we get that going.

Once we are making the bifilar loop balls ourselves, the obvious next step is to make a bigger Newton’s Cradle.  Two inch balls are available from Educational Innovations , sold as a demo of mechanical energy converted to heat.  Scaling up the frame is straight forward machining project.

Surprising to me, no one makes this.  I mean, there are giant versions of Newton’s Cradle, many made out of bowling balls, and you can easily find them on, e.g., youtube.     They are all pretty lame.  Problem is, the coefficient of restitution of a bowling ball is very small compared to that of a ball bearing.   No bounce, which makes sense because you wouldn’t want your bowling ball bouncing down the lane toward the pins.   The Bowling Ball Newton’s Cradles end up rapidly degenerating into an all ball swing. Ugh.

When we have the big version going,  we will rule the youtube Newton’s Cradle videos.  Oh, yeah, we have a youtube channel, called NatSciDemos, I think, but I can’t check because I’m done for now.

Good to get writing again.  Now I  go to bicycle commute with my daughter, who’s working at the uni. for the summer.

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Holiday lecture redux: Germs.

The theme of last year’s holiday lecture, given twice at Harvard and once at Princeton, was Germs: A Detective Story.

The main part of the talk was about Dr. John Snow, who proved that Cholera is a water-borne illness caused by a bacterium. From the time he began to suspect this to the time he proved it scientifically was thirty years.   In the meantime, he only drank distilled water.

The scientific consensus at the time was that a miasma caused cholera, that is, the stink of raw sewage and dead animals and garbage.   Of course, conditions where “bad air” was present are also where the water would be contaminated, so the possible causes were confounded.  London in the 1850′s was a funky place, but it turned out that water delivery was tightly controlled by a few companies.

One neighborhood had two delivery companies, one which took water from upstream Thames, and the other from downstream.  The water downstream was contaminated with sewage, and also with small amounts of salt, from the tidal infiltration of sea water.  To the eye and taste, the two waters were the same.  The downstream water, John Snow thought, was causing cholera.

From house to house he went, asking about cholera in the household, and asking which water company delivered the water.  If the respondent didn’t know which water company served the house, which was often the case, he asked for a sample of the water.  Later, in the lab, he would add a few drops of silver nitrate solution to the water.  The upstream water would remain clear, but the downstream water would form a precipitate of silver chloride, making the water cloudy.

From this survey and experiment, he found that 90% of the cholera cases came from houses using downstream water.  Since all of the houses experienced the same “bad air”, John Snow demonstrated the connection between bad water and cholera.

For the holiday lecture, I started with two glasses of distilled water, and added salt to one, while the lecturer turned his back. With the water glasses shown up close on the video projection screen, I added a pipette full of silver nitrate solution to each.  The salty water showed a massive precipitate of silver chloride, much more than John Snow would have seen, but perfect for a demonstration of how two identical looking glasses of water can be very different.

The story of John Snow can be found in the book, The Blue Death: The Intriguing Past and Present Danger of the Water You Drink by Robert D. Morris  .   He was on his way to being as big as Koch and Pasteur, but tragically died in his forties.

The other demos were microscope based.  A video signal converted to VGA and then projected lets everyone see the microscopic world writ large.  Working live made the experiment an active experience for everyone.

The first sample was saliva, which came from the kids who volunteered to come down and spit in a tube.  Five kids came down and spat in 50 ml plastic centrifuge tubes, and then screwed on the tops.  I picked one at random and swabbed some of the saliva on a microscope slide and dropped a cover glass on it.  A 40x objective gave a 0.2 mm horizontal field of view.  Cheek cells were visible, the size of (American) football on the screen.  Motile bacteria were always there, wiggling and swimming about, and with thirty seconds of viewing everyone was ew-ing and aw-ing.

The other microscope demo looked at red blood cells and how they were affected by either saturated salt solution or distilled water.  The blood came from my finger, pricked with the spring loaded needle from a blood sugar testing kit.  The drop of  blood went into a milliliter of normal saline, about 0.7% w/w, and mixed well.  That diluted the red blood cells so that they were individually visible on the slide.  A tiny drop of the diluted blood went on a cover glass, which was then inverted onto a prepared well slide.  The drop didn’t fill the well, leaving room for added solution to wick in and act on the red blood cells.

Saturated salt solution collapsed the red blood cells, turning them from donuts into sickles and then crumpled blobs.  Distilled water ballooned the red blood cells, which rapidly faded as they burst and leaked their contents.  After that, the only cells easily visible were white blood cells, which also ballooned but are tougher, so it took longer for them to burst.  I saw a few pop, very cool to see cell guts spewing out.

What did osmosis have to do with bacteria?  Penicillin kills growing bacteria by installing pores into the cell membrane, so the same action that burst the fragile red blood cells could pop the tough bacteria.  We showed this: Movie of staph being killed by penicillin. 

I learned a lot, and got all jazzed about bacteria.  Bacteria are all around us, and in us.   I’m reading A Field Guide to Bacteria (Comstock Book) by Betsey Dexter Dyer  which is just super.  A few pointers on microscopy, but the main focus of the book is the macroscopic indications, or field marks, of various kinds of bacteria.  I’m just loving it.  Kimchee and yogurt in the fridge, wine turning to vinegar on the counter, all bacterial field marks.

The t-shirts were: Blue for Water, the wizard of osmosis. Purple and orange for  Silver Chloride, if you’re not part of the solution, precipitate. Crimson for (cartoon image of lipid bilayer), osmosis, it’s swell.  Volunteers got a green shirt with anthropomorphic staphylococcus, Volunteer Staph, our enthusiasm is contagious.

The t-shirts are used to differentiate the kids for playing molecules in short molecular simulations.  The kid molecular demonstrations were of silver chloride precipitating, and of cells (ring of kids wearing lipid bilayer shirts) swelling and shrinking in hypo-tonic and hyper-tonic solutions.   Pretty sophisticated stuff to act out, it was well done and fun to watch.

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Precious metals

{copper, silver}, {copper, gold}, {silver, gold} are fairly well known examples of binary alloys.  Most jewelry is an alloy of these pairs, with a few other metals added in some proportion, intentional or not.  Even when you buy the pure element, there is some fraction of impurities.  A good and well studied system to admire and experiment with.

I was going to point you at a modeling site, with an uploaded molten gold in a box model file, but I just  crashed my browser so I’d better go.  The software is Molecular workbench, the company is Concord Consortium, and the website is www.concord.org/modeler.  The code is a work in progress and has been known to be crashy occasionally.  Very worth figuring out.

Lots of demos sweep me off my feet and then are put away before I think to write about them.  One that we do tomorrow it to break a wooden beam, 1.2 cm x 1.5 cm by 145 cm, which is supported on each end by a raw egg.  The eggs are set on end on tables separated by 140 cm, and are stood up in a small wad of plasticine.    The beam rests on the eggs’ tops only, and spans the space between the tables.  The performing scientist swings a metal rod down at the center of the beam, which done right breaks the beam quickly enough that the motion of the ends is upward.  The broken pieces each rotate around their own centers of gravity, and the eggs go unbroken.

We shall see.  There are three beams, and a dozen eggs.  What could go wrong?

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Exploding mouse red blood cells

I suppose I’m taking a chance, what with the law about visualizations of animal cruelty still under consideration by the Supremes.   I feel a little cruel making my dog sit and wait (and drool) for her dinner, so I’m not being flip about this.

I brought our crufty video enabled microscope over to Pfizer lecture hall over in the Mallinckrodt building.  (Who pays for these place names?  Oh, yeah.)  A video projector was set up on the side screen, with the main, center screen for the professor’s powerpoint.  I prepared a microscope slide as follows in the scanned notebook page:

A way to add solutions to a sample under the microscope.

The procedure for mouse blood is the same as for cheese, except substitute mouse blood for milk, and hypertonic salt solution and distilled water for the acetic acid.  With a pipette, a very small drop of mouse blood  is placed on the slide, and the cover glass put in place.  First with the 10x objective, and then with the 40x I focused on the blood.

In fact it is really hard to see individual red blood cells in a thick sample of blood.  The parafilm is thick, makes a deep well.  Putting the cover slip down on the drop of blood, which smooshes the drop flat, makes the individual red blood cells easier to see.  Next time I think a sample of blood diluted in normal saline would be better, and would allow us to see the normal red blood cells more clearly before shrinking them in concentrated salt solution, or inflating them in distilled water.

Flood the sample with distilled water and watch the red blood cells swell up into little balls.  Using a straight razor blade, cut a channel from the side to the well.  The cover slip is over the well and half of the channel.  A drop of water placed on the channel wicks into the well.  Everything microscopic zooms around for a second, then stop.  The osmotic action is pretty fast at this scale.

With milk and acetic acid, the action is a little slower, as the protein forms filaments that lock the fat globules in place.  The fat still jiggles, but the globules don’t move around anymore, after about a minute.   Microscopic cheese!

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Ig Nobel Moments of Science

The Ig Nobel Awards Ceremony is happening tonight at 7:15 in Sanders Theater at Harvard University.   My friend and co-conspirator Joost and I will once again don our lab coats as Performing Scientists, and perpetrate two Moments of Science.

Each Moment of Science is a one minute science demonstration, presented and acted out on stage.  As with the IgNobel prizes, the goal is to make people laugh, and then think.

The ceremony is streamed live at http://improbable.com.

Moment number one is a presentation of the kinetic molecular simulator otherwise known as the Golfball Atmosphere.  I mentioned it in the last post.  Some of our best Moments come from the recent demonstrations done for physics classes.  This time, it uponned my mind to use this demo just as we were meeting to rehearse the second.  I was despairing of the first choice.  We planned to somehow put a whole bunch of pre-set, Victor mousetraps on a surface and throw ping pong balls at them to set them off.  Aside from an impractical set up, long and risky, it just wasn’t going to work very well.   A good argument for coming up with ideas for performances after a few beers is those practicalities are swept away in a cheery glow.

Walking through the basement toward the lecture halls, I pictured the Golf ball Atmosphere, and I knew it was the right choice.  I showed it to Joost, and he agreed.  Simple, loud, bright and fast moving.   I’d better go and clean it.  The ceremony starts in a few hours.

The second Moment is inspired by Roy Glauber’s demonstration of a Tesla coil for Science A29.  The coil is small, about a meter tall.  The high voltage source is on the bottom of a cart, with the Tesla coil on top.  Rolled out and  plugged in with a flourish, it bursts into action with a loud buzz and blue sparks.  A spark gap in front breaks down and the primary coil rings with the glass plate condenser, and the secondary, a tall tube wrapped in fine wire, is driven at about a megaHertz, a few hundred thousand volts of AC voltage.  Enough to light a fluorescent light tube.  The current flows from the top of the light tube to the nearest hand, thence over the skin and to ground.  By moving that hand up and down, the lit part of the bulb changes in length.  So I will be stroking the glow bar.  Huh huh huh.  Fortunately, masturbatory humor is practically required at the Ig’s.  We hope to have the V-Chip censor flag us down and stop the Moment before it gets out of hand.  Huh huh huh.

Anyway, it is all going live on the web at 7:15 pm tonight, Thursday October 1st, 2009.

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Gas laws

Today, the physics professor was demonstrating centripetal force, by swinging a bucket around and not spilling the water within. Then, to up the ante, he put a wineglass full of faux wine on a small board made like a swing.  He got it going, and whipped it around four or five times before the wineglass became unstable and flew off.  It flew in a straight line, right into the wall.  The only piece of glass bigger than a dime was the stem.   (Faux wine is six drops of red food coloring and one drop of blue in a wineglass of water.)

The evening school is doing gas laws. PV = nRT.   or PV = NkBT.    Both sides of the equation are energy.  Yow!

Our golf ball atmosphere is loud and goofy, a perfect example of what we used to do before computer simulations got so good.  A turntable with paddles whacks plastic practice golf balls around a glass box, with a wire screen lid that is counterweighted to about twenty grams force down.  All that random bouncing pushes the screen to the top of the glass box.  Did I say loud?  What?

A shaking jig for bb’s shows some more physical analogy of thermal motion.   A fifteen centimeter window covered by a petri dish, shaken by three speaker drivers, pushed by a massive bipolar power supply/amplifier, driven by a Pasco signal generator.   All on an overhead projector, and projected on the front screen.  Gotta be three or four kilobucks of equipment there, and no substitutions work.  I love that Kepco amp.  Sigh.

Balloons and boiling water, balloons and liquid nitrogen.  Like a dangerous birthday party trick, but really all about the T for temperature term in the equation.  Helium balloon collapses, carbon dioxide balloon shrivels up completely.  Boiling water is only four thirds as hot as room temperature, so a balloon fitted to the beaker will swell up, but just enough to make the point.  Liquid nitrogen is one quarter of room temperature, enough to make the helium balloon sink in air, until it warms up and floats away.

Fifty five gallon drum on a vacuum pump, no surprises there.  Marshmallows in a bell jar swell up three fold, and then relax to normal size while the vacuum pump keeps working.  Let the air back in and the marshmallows turn into an hourglass shaped raisin-like object.   Working the P for pressure angle of the gas law equation.

Three plastic soda bottles with 100 ml of vinegar stand with balloons on their necks.  In the balloons are five, ten and twenty grams of sodium bicarbonate, ready to be dropped into the vinegar by raising the balloons.   That speaks to the n of the equation, or number of moles of gas produced.

An old wooden organ pipe is blown with air, helium and sulfur hexafluoride.  Speed of sound in each of the gases affects the pitch of a pipe, said pitch being the standing wave that fits the pipe.

A tub of water with a cylinder is there to catch gas by displacement of water, just as a lab demo.

A plastic water bottle with a fine mesh screen on the bottom holds a liter of water just fine.  In fact, you have to shake the bottle to get any water out.  Or you could open the screw top and let air in, splash, mwahahaha.

That is a lot of demos.  I am tired.  I hope the night crew is willing to put all these things away, because I do not want to wait until 9:30 to go home.

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Hey, where did the categories go?

Must have been the upgrade to wordpress.  I liked the categories, I guess I will put them back in.  I can go over my ouevre and re-assign.  I haven’t hit 100 posts yet, so its not that laborious.

Physics demos today.

A rigid pair of verticals and a horizontal clamped up to make a suspension for a 1.00 m pendulum, with a 30 mm brass ball as the bob.  The bob can move in two directions, making it a circular pendulum.

A 65# wrecking ball is suspended from the ceiling skyhook with wire rope.  The physics victim takes hold of the ball, and walks backwards to the blackboard, drawing the ball up to his chin.  With head against the blackboard, the victim releases the ball.  It swings out as a pendulum, and then swings back in.  Conservation of momentum predicts the wrecking ball will not hit the chin.  The owner of the chin can be forgiven for flinching.  The ball returns to within a centimeter of its release point.  It is a viscerally impressive lesson in physics.

How much equipment does it take to measure little g, by dropping an apple from the ceiling of the lecture hall?  A lot.  I’ll post photos on Thursday when we do it again for another physics class.

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Classes begin tomorrow? Where did the summer go?

I could use another week of Atlantic City, NJ.  The surf off of the Chelsea Ave. beach was stellar, and I want more.

The torrential rains of two days filled the area between the boardwalk and dunes with brackish pools.  The wind whipped waves moving from the left of a walkway found only a one foot gap to get by, and on the sheltered side on the right, formed an enormous single slit water wave experiment.  Beautiful.  Alas, I was running and had no camera.

At least there are demonstrations to do tomorrow.  For Life and Physical Sciences A, at 9 am:

Green balloon with helium.  Blue balloon with hydrogen.  Candle on end of stick, matches to light.

Plus liquid N2, soda bottle and trash can.

Also, some elements : Sulfur, Copper wire and copper powder and copper bar, Zinc, halfnium, germanium. And some cupric chloride.  Is there any way I could test the conducitivity of these materials?

Off to make the demos.

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