Surprising Science Demonstrations? 640
An anonymous reader writes: "I have been called upon to conduct some science workshops for children of various ages, and I'm looking for some good demos. In particular, I've found that demos are most effective at getting students to think when they give a surprising or unexpected result, such as the classic two-slit experiment (or, for the extreme crowd, demonstrating the Leidenfrost effect by sticking one's hand into a vat of molten lead [PDF]). I'd like the Slashdot crowd's suggestions." Please don't do the lead one.
Baking soda and vinegar (Score:5, Insightful)
Re:Baking soda and vinegar (Score:5, Funny)
I always had fun loading hydrocloric acid into a supersoaker-100 when I was a kid. You can buy it at any pool store. I could make nice messages in people's lawns with it.
Boy did I confuse the hell out of me ex-girlfriend when I wrote "I'm a dyke" in 15 foot letters into her lawn. She wondered how I did it since it was written in such nice cursive. I denied everything of course since her dad would beat the sh*t out of me. Its also fun to shoot at metal objects with it. I rusted a stop sign and broke off the pole in just 3 minutes. I had my supersoaker pumped high and I shot it with alot of pressure. The poisionous gas clouds that mist outward from the gun kind of suck though. Yes it can sting and burn your lungs.
I am glad I matured beyond this. However if I lived in Redmond Washington, I would probably still have alot of fun doing this.
Re:Baking soda and vinegar (Score:4, Informative)
Re:Baking soda and vinegar (Score:3, Interesting)
Re:Baking soda and vinegar (Score:2, Funny)
Hey, guess what, the stinging and burning was just a symptom of the problem. The problem was that you damaged part of your lungs while inhailing those fumes at close range.
Although you don't quite qualify for the darwin awards...
Re:Baking soda and vinegar (Score:4, Funny)
Oh, come on, isn't there some kind of Darwin Honorable Mention that we can give him? Lord knows he deserves it....
Re:Baking soda and vinegar (Score:4, Funny)
Yes, I have a big yellow pin-on button for him that says "Me Stupid".
Re:Baking soda and vinegar (Score:5, Interesting)
We also tried the Binaca [scitoys.com] cannon. (The kids also went nuts with Ace Ventura jokes
And, yes, my homeowner's insurance is rather pricey...
Re:Baking soda and vinegar (Score:5, Interesting)
Better yet, magnesium, fire, and water. The 5,000 degree flame dissassociates the water molecules into hydrogen and oxygen. Fun.
Also, drano and tinfoil produces hydrogen. The best way to do it is to put lye powder (seems to work better than drano for me), water, and tinfoil in a PLASTIC gas can. Then, attach the nozzle to a hose. The whole thing will heat up and send noxious steam and hydrogen through the hose. The bad stuff condenses in the hose and you are left with very pure hydrogen.
You can mix the hydrogen with some air to make it explode, or you can let it float. Also, you can breath it. That produces a similar effect as helium
Re:Baking soda and vinegar (Score:3, Interesting)
Uncover the hole, and a small tube-like stream of water will come out. You can see the laser light bouncing through it in a fiber-optic effect, and the place where the stream hits a surface will glow.
Warning: this may generate future fiber-optics engineers as a side-effect: use with care.
be damned careful about that one... (Score:5, Funny)
that same teacher showed us a kinda cool experiment herself. drain about 1/4 of the coke out of a 2-liter coke bottle, and drill a very small hole in its cap (the smaller, the better). next, take about a roll of mentos (the original kind, i think, test it out yourself), and place small holes through the center of each. now take some fishing wire and thread them through all the mentos in a line, and tie the ends with something heavy like steel nuts. make sure the mentos are tied together tight, and give a little extra fishing wire on one side. thread this extra fishing wire into the bottom of that coke cap with the hole in it, and screw the cap on the coke bottle, holding the fishing wire to make sure the mentos do not touch the coke inside. drop the wire to let the mentos drop into the coke, and move out of the way. some odd reaction takes place that causes the cap to shoot off and hit the ceiling, and pop spews close to 10 feet in the air. at least, thats what happened when my chem teacher did it. the janitor was pretty pissed that he had to clean the ceiling after that one.
alternately, you could just offer someone a coke while theyre eating several mentos :)
No explosions (Score:5, Informative)
I much rather like demonstrations that are counter-intuitive. Especially things that seem "supernatural" to do, yet are very natural indeed. I'd like to point out the work of David Willey, whom I've worked with. He organized a world-record firewalk, and I attended (yeah, I've got a world record in firewalking... :-) ).
Check out his article in Skeptical Inquirer: The Physics Behind Four Amazing Demonstrations [csicop.org].
David has done quite a lot of explosions and rocketry too, he knows all about that too, but his best demos is really those that seem risky, but are not. The liquid lead is among them.
Re:Baking soda and vinegar (Score:3, Interesting)
M@
Re:plasma ball (Score:4, Funny)
Re:Baking soda and vinegar (Score:3, Informative)
I remember in chem class chunking the crust off the H2O2 bottle, and turning my finger tips white just from that (with out getting any moisture on my hands), because the stabilizing agent was so good that even dried there was still plenty of H2O2.
Here's a nice, simple one. (Score:2, Informative)
It's funny to watch.
Re:Here's a nice, simple one. (Score:3, Interesting)
The teacher couldn't find an appropriately sized beaker or test tube so she used a chemistry bottle - I.E. one with a narrow neck.
She put powdered sugar in the bottom and poured the sulphuric acid in, and everything went as planned, until the carbon compressed in the narrow neck and got stuck - forming a plug.
Of course, the reaction was still going on in the bottom of the bottle - creating pressure along with additional carbon. Eventually the pressure built up enough to blow the previously-stuck carbon out, all over the ceiling and the front row of tables. Fortunately, noone got covered with hot acid.
Last time I was in that room I could *still* see the melted part of the fluorescent light fixture which was right above the expiriment (They replaced the blackened ceiling tile). I also remember that all year we'd get a chuckle whenever someone who was on that front row would open their science notebook and see a burnt hole in the middle of their pages.
Yes, I'd say that was a good learning experience... :)
ammonia fountain (Score:3, Informative)
Hot Wax (Score:5, Informative)
Another one my chem teacher did was taking water and separating it into oxygen and hydrogen by using a battery and matching the terminals, then letting the hydrogen into a test tube and light it to make a loud "pop!"
Also, anything that disolves metal with a liquid is good, like magnesium and acid or such.
Re:Hot Wax (Score:3, Insightful)
Re:Hot Wax (Score:5, Interesting)
Set the match on the edge of a table, head pointing accross the room. Then heat the match head with another, lit match.
The foil prevents the match head from lighting; The heat induced by the other match causes a reaction (small explosion) that sends the foil accross the room like a light-weight bullet.
DISCLAIMER: I am NOT responsible if someone gets burned or maimed or you get your or someone else's eye poked out, trying this stuff.
Re:Hot Wax (Score:4, Informative)
You can even make the paperclip into the launchpad.
Here is some other designs:
http://www.matchrockets.com/fire/mr.html [matchrockets.com] - This one has Video and info on calculating velocity!
http://users.bigpond.net.au/mechtoys/matchrocket.
http://www.grc.nasa.gov/WWW/K-12/TRC/Rockets/matc
http://mrockets.hypermart.net/brett/ [hypermart.net]
http://www.reachoutmichigan.org/funexperiments/ag
Re:Hot Wax (Score:3, Informative)
Maybe this isn't the best for little kids, but it certainly was interesting. Another cool one was when he made natural gas bubles and poped them with a splint on fire. Very cool looking effect. One last (and very invoulved) idea is to make an oscilating reaction. This takes a lot more prep, but you could have the different solutions pre-made, and just mix them in front of the kids.
some good ones (Score:5, Informative)
1: Using compressed air to shoot a pencil through a peice off 1/2 inch thick plywood
2: Using a large solenoid to magnetically rip apart an aluminum can (can is placed in the center of the circle of wires and large AC is momentarily applied)
3: Pouring liquid nitrogen on your hand (the back, not your cupped hand)
4: Making liquid nitrogen ice cream (pour some LN2 into a cup of milk, stir rapidly)
5 Superconducting magnetic levitation (small permanent magnet over a critically cooled superconductor)
6:The ever classic fire extinguisher used to propel a person across a room in a rolling chair
7: compairing the explosions made by a baloon filled with air and h2, h2, and one with both H2 and O2 in proper amounts
Re:some good ones (Score:3, Informative)
sweet! i want to try that one. or any of these [angelfire.com].
Re:some good ones (Score:2)
it is very loud and puts out a prety good shock wave.
Re:some good ones (Score:2)
This would dovetail nicely with the molten lead demonstration.
Re:some good ones (Score:5, Funny)
This would dovetail nicely with the molten lead demonstration.
And, in all likelihood, you could wrap up the session with the ever-popular "trip to the emergency room" demonstration.
Re:some good ones (Score:3, Interesting)
Of course, toward the end of the book a certain revelation is made that puts Twirlip's comments into an entirely different light. Vinge has been overheard saying that, in fact, Twirlip was the only character in the book to really understand what was going on. He was being mistranslated, but only slightly, and not at all in the way that the other characters thought.
He's my hero.
Re:some good ones (Score:4, Informative)
Re:some good ones (Score:3, Informative)
Liquid Nitrogen Ice cream (Score:5, Interesting)
Re:Liquid Nitrogen Ice cream (Score:3, Insightful)
And what about girls? They really are not interested in the destructive side of things. I like this ice cream one. Everyone likes ice cream. Parents won't freak out when their kids come home with a new way to make a snack, but watching Junior shoot a can across the living room is sure to rile them. Or how about something from CSI? Forensic science is becoming extremely popular and many public schools are beginning to integrate it into their curriculum.
Collection of Chemistry Demos (Score:5, Informative)
Re:Collection of Chemistry Demos (Score:4, Informative)
Check it out -- I remembering him (and some graduate students) putting a lot more effort into the actual presentation than he does into the webpage...
Re:Collection of Chemistry Demos (Score:3, Interesting)
See the photos here [purdue.edu]!
Levitation thing (Score:2, Informative)
(or do something along those lines...)
Microwave of Course! (Score:4, Informative)
1: Lightbulb, metal in milk to insulate, don't use anything with mercury in it.
2: CD-Rom (all kinds work, try different ones)
3: place a toothpick in a peice of cork, place in center of microwave, place 3 peices of cork around center cork and support fishbowl(any peice of glass that is globe like will work, the more like a globe the better) light the toothpick, place glass on top of corks around edge(for ventilation) and start microwave
4. grape, cut the grape in half, then carefully slice the grape again in half, but leave small peice of skin connecting quarters. Fold together to make a flat side and place on microwave floor.
Hints: use old microwave, preferably with clear front faraday cage setup, in addition to this also place a glass of water in the back of the microwave to avoid destroying the magnetio. Tinfoil and other items are fun too, play around and have fun. Ohhh yea, no gerbils etc. Have fun.
Re:Microwave of Course! (Score:4, Informative)
sodium explosion video (Score:3, Informative)
angular momentum; hands-on stuff (Score:5, Informative)
But better than a demonstration is anything hands-on, especially with young kids. You can do some cool stuff with the new neodymium magnets. You can hook up an oscilloscope to a microphone and let them look at their voices. (Or use computer oscilloscope software.)
Leidenfrost demo. (Score:3, Informative)
Ah yes, this would be the one where the paper says, "Never, ever do this.". [If you use too much water, you get a steam explosion that sends molten lead everywhere.]
You might be able to do a safer variant by dipping apples or bananas or what-have-you, though, with a blast shield between the crucible and the audience, though (and a leather apron and gauntlets and visor, unless you *like* liquid metal scars).
Re:Leidenfrost demo. (Score:2, Funny)
My personal favorite (Score:2, Insightful)
You need a copy of ... (Score:2, Informative)
The book is chock full of science-geekly fun. The demonstrations are clear and exciting. Kids will love them. The accompanying explanations are in-depth. If you do them all and learn why they work, you'll soak up a fair amount of physics.
Here's a classic (Score:5, Informative)
Suspend a cinder brick (or other heavy object) from the ceiling with a rope. Pull it back until it just touches your forehead and let go so it swings like a pendulum. It you don't move, it will just touch your forehead on the return swing (or a little short of it). Listen to the gasps of horror from those in your audience who think your head is about to be smashed.
Re:Here's a classic (Score:5, Funny)
Re:Here's a classic (Score:3, Funny)
Easy way out. Just say,
"I made a crater on my face on purpose because today is Astronomy Day, kids!"
Re:Here's a classic (Score:3, Funny)
Other possible problem (Score:5, Informative)
Re:Here's a classic (Score:4, Funny)
Moral of the story--Flying bowling balls have a considerable amount of momentum, and they hurt.
Demos Galore (Score:2)
Aluminum pipe and magnets. (Score:3, Informative)
One I found interesting involved a long aluminum pipe a steel cylinder just small enough to fit in the pipe and a cylindrical magnet (or cylider containing a magnet) of the same size.
First demonstate that the magnet is not attracted to the aluminum by pressing against the pipe.
Then drop the steel slug through the pipe. It should slide through unhindered and quickly fall out the other side.
Now drop the magnet through the pipe. The moving magnet will induce an electric field in the pipe which in turn induces a magnetic field and slows the magnet. And hence it falls very slowly.
Then of course there are the two syringes of different diameter coupled by a plastic tube to illustrate hydraulics.
Re:Aluminum pipe and magnets. (Score:3, Insightful)
friction demo. (Score:3, Interesting)
Or you could stick some flys in a microwave. They live because their bodys are to small to absorb the radiation. This one really needs a kitten to set up with though....
Science for Kids (Score:5, Interesting)
First one was chemistry. Did a mixture of hands on plus some interesting demos. Hands on was stuff that was designed to be SAFE - indicators, baking soda and vinegar, etc. Demos were designed to be visually interesting. Burning magnesium, volcano (ignite ammonium dichromate), thermite, fun with liquid nitrogen. (Keep the kids WELL BACK for these). The kids loved it.
Second one was on crypto - simple encoding, decoding, and cryptanalysis (breaking caesar cipher by brute force, and substitution cipher by letter frequency analysis). Kids were divided into teams of four for a set of exercises. One of the teachers told me the kids were passing encoded messages in class for weeks afterwards.
Make sure the kids have fun AND learn something and you'll be successful. Good luck.
I forget what it is called (Score:2)
it was pretty cool.
Lots of things: (Score:2)
Crushing cans: There are several variants, but the cheapest one involves putting some water in the bottom of an otherwise empty soda can. Boil the water until you see steam coming out. Then, quickly tip the can over in to about an inch or two of cool water.
Mag-Lev: find an aluminum pot lid. Everyone knows that aluminum isn't magnetic, right? Well, rig up the lid so that it's attached to a drill. Take a small disk magnet (rare earth works best) and attach it to an armature (easiest way is to take some sort of steel latch or hinge and just stick the magnet to it). Spin up the lid, and hold the magnet over it with the armature. The key is that if it weren't for the mag lev effect, it would fall on to the pot lid.
Angular momentum: Student + weights they can hold + disk they can sit on and spin = good fun. Show them how pulling the masses is speeds them up, and holding them out slows them down.
There's a whole lot more, but that's all I can think of right now.
BlackGriffen
Combustion demonstration (Score:2)
Spontaneous combustion (Score:2, Interesting)
Take a test tube, put in a little piece of cotton, then get a sealed plunger (they make kits for this). When you take the plunger at the test tube, the air pressure increases enough to cause spontaneous combustion.
Magnetic rail gun
This one's pretty simple. Tape a few magnets (preferably neodynium) across the central groove of a plastic 12" ruler, spaced evenly apart. Place small steel ball bearings to the right of each magnet. At the very left of the ruler, let a small bearing roll towards the first magnet. The one on the very right will take off at a decent speed.
Shattering glass with sound
For this you'll need something that can make a pretty loud tone at a given frequency. Take a glass jar or beaker, and tap it with an eraser or something to find the natural frequency. Then use a tone generator to blast that natural frequency at the glass. Given enough amplitude, the glass will shatter (not explosively).
Centripital Force
Build a circular horizontal track, and drive an R/C car around it, sideways.
Stab a Paper straw through a raw potato (Score:3, Insightful)
you can jab it through a raw potato like a dagger.
Sealing the end allows the air pressure to build up and make the straw super rigid.
Re:Stab a Paper straw through a raw potato (Score:3, Funny)
For chemistry (Score:2)
One of the more surprising experiments I rememberd from high school where the teacher took two perfectly clear liquids--water, for all we know--an poured them together. They instantly turned a bright, fire-hydrant yellow. There were gasps all around the room.
I don't remember what the two substances were, but I seem to recall that one was lead-based and the lead combined with something else to form the precipitate (it later settled to the bottom, I think).
I'm sure any competent chemist, especially one in the paint industry, should be able to point you in the right direction for something like this.
My personal favorite experiments are those where I personally confirmed some fundamental property of nature. I've ``proven'' that absolute zero is about minues three-fifty Fahrenheit; distinguished lead shot from iron shot from tin shot by calculating their specific heat; and measured the speed of sound using a tuning fork.
Don't just tell the kids some fact. Give them the chance to prove it for themselves.
Cheers,
b&
Physics Demo -- Kinetic Energy (Score:5, Interesting)
Momentum, actually (Score:5, Funny)
I've also done this demo with three balls stacked on each other. It's much harder to get them all aligned, but when it works, the topmost ball goes (optimally) forty nine times higher than when bounced alone.
Note that the momentum conservation equations that give the perfect reversal of relative velocity assume that one object in the collision is much more massive than the other (i.e. basketball versus earth and tennis ball versus basketball). In this limit, the velocity of the more massive object is essentially unchanged by the collision.
Once, for fun, I calculated that if you extended the stack of balls to something like 20 that the topmost ball would attain orbital velocity
Re:Momentum, actually (Score:3)
Take a large peice of PVC piping (correct diameter of basket ball) drill a small hole into the pipe and use a nail to hold up the balls. (put balls in before you stand up the pipe) stand up the pipe and remove the nail. (might require using a little double sided tape or something to hold the balls together on the descent). If this really will acheive orbital velocity then you will surely impress all the kiddies.
Re:Momentum, actually (Score:3, Insightful)
Sure, for a demo with only 2, a basketball and tennis ball do the trick. For 3, you could probably use a ping-pong ball as the 3rd. one.
You quickly reach a point where you run out of useful objects though. With 20, what's the size of your ball on the bottom? A small meteorite?
Stupid Physics Tricks (Score:2, Interesting)
1 - Spewing liquid nitrogen. WARNING: I've done this but if you screw it up it is your own fault and will HURT YOU. It is possible to take a mouthful of LN2 then immediately spray it back out in an impressive cloud of vapor. This works because a tiny layer of LN2 vaporizes when it hits your tongue, thereby insulating you from the LN2. This effect is very short-lived and you can FROSTBITE YOUR TONGUE if you don't immediately spew it back out!!!
2 -- Balloons in a trash can. Put 1 inch of LN2 in the bottom of a trash can (you *might* get this to work with dry ice -- easier to come by). Ask the audience to guess how many balloons will fit in the trash can (don't let them see the LN2!)Begin dropping balloons into the trash can. The balloons will shrink to a fraction of their room temp size as they cool down. Think "clowns in a car" for geeks.
3 -- Bed of Nails. I've lain on a bed of nails built out of heavy plywood and standard nails. This takes work to build: the nails MUST all stick out exactly the same distance through the wood, and you should remove any burrs or extremely sharp tips. I *believe* we used nails on a 1 inch grid (which was overkill for safety). USE A PILLOW! Your head is heavy and ROUNDED -- it will end up supported on only about 4 nails: NOT ENOUGH. You may want to do a little research to get the optimal grid size "nailed down".
4 -- Corn starch solution: Cool stuff. Under pressure a thick corn starch solution will act like a solid. Without pressure it is a liquid. Fill a pan with it, demonstrate that it flows, then (with viewers gathered around) slap your hand into it hard. They'll expect a splash that never comes. This works because corn starch is a long molecule that curls under pressure, interlocking the molecules into a "pseudo-solid". Throw it back and forth like a ball. Don't pause, though: the impact with your hand will keep it solid only for a second before it "melts" again!
5 -- Get a large piece of Transparent Aluminum, a sonic screwdriver, and a tribble.
Actually, that one tends to offend squemish members of the audience, so we'll skip it here...
Flourescent Pickle (Score:5, Informative)
- Get a lightweight, 2-prong extension cord.
- Do not plug it in yet.
- Bare the ends, and wrap them around two medium-large nails.
- Insert the nails into the pickle.
- With all hands off the pickle and the bare metal, plug in the cord.
- Observe that the pickle glows around the contact points with the nails.
Caution:- Never tough the pickle or the bare metal while the cord is plugged in: shock hazard (duh
:-)
- Put the pickle on a non-conductive surface, e.g. sheet of wood.
- Consider doing it out doors, as it smokes and is smelly.
- Adult supervision required. You assume all risk.
Crispin----
Crispin Cowan, Ph.D.
Chief Scientist, WireX Communications, Inc. [wirex.com]
Immunix: [immunix.org] Security Hardened Linux Distribution
Available for purchase [wirex.com]
Re:Flourescent Pickle (Score:3, Funny)
Extra credit for anybody who eats it when done.
Re:Flourescent Pickle (Score:3, Funny)
Do this outside or in a well-ventilated area. Do not chase your guests out into the cold dark night. Well, it was Pasadena, CA, so it wasn't that cold, but still -- beware the stinky pickle.
Also beware the stinky, half cooked pickle after it's sat out on the deck for the next month.
Re:Flourescent Pickle (Score:3, Funny)
I had a chem lecturer who did just this very demonstration as a fun way of introducing emission spectra (pickles contain high quantities of sodium, making the pickle act like a sodium lamp). As the demo wore one the glow from the pickle decreased, presumably because some chemical change in the pickle wrought by having large quantites of current pumped through it tied up the sodium. To compensate, the lecturer cranked up the voltage on the power supply he was using, which worked fine until his hand slipped and he accidentally ramped the voltage all the way up to the supply's highest setting (240V IIRC).
Needless to say, this was well in excess of the pickle's tolerances, and it exploded, showering fat orange sparks everywhere (nearly catching an unlucky student volunteer involved in the demo) and sending an almighty stink throughout the lecture theatre. So bear in mind that a pickle has exactly the same limitations as any other electrical component when doing this experiment.
Ah, first-year chem, those were the days. Exploding pickles, naked guys wandering into lectures...ahem, exucse me, I digress...
Cool demos I've seen. (Score:5, Interesting)
To do this, put some sugar in a beaker under a fume hood and use tongs to pour a bit of concentrated sulphuric acid on it from a second beaker. The acid catalyzes water extraction from the sugar (which is exothermic), giving you a big mass of carbon puffed up with steam. This sponge is much larger than the original sugar sample (demo looks coolest if this greatly overflows the beaker; you get a column of carbon coming out of it).
Handle the acid with great respect, as it'll eat through anything organic or metallic. Phosphoric acid probably works for this too, though I haven't seen it done.
Inflate a balloon, tie a string to it, and then lower it into a dewar of liquid nitrogen. As the balloon approaches the nitrogen, the air nearest it cools and becomes a lot more compact (remember gas laws). What you end up with is something that looks like a deflated balloon, with either very cold air or (if you dunked it) liquid oxygen and nitrogen in it. Leave it on a counter, and it may re-inflate (try not to freeze all of the rubber if you want it to do this).
Dip just about anything containing water into liquid nitrogen, and it turns into a rock. Do this with something fragile, like a flower, and you get a flower that shatters as if it was made of glass when you tap it on a desk. This is very impressive.
I've heard of someone dunking a banana and shattering it with a hammer, but you'd have to leave it in for quite a while to make sure it's good and cold. When I tried similar things, the ice deformed instead of shattering.
This one only works if you have a high-powered laser handy. I suppose in a pinch a sufficiently powerful ordinary light source would do too. Stick a coloured balloon inside a transparent one, inflate the inner balloon half way, tie it off, and then inflate the outer balloon fully. You end up with a coloured balloon inside a transparent one. Shine a laser or other very bright, localized light through the balloons and the coloured balloon will have a hole melted in it and pop, leaving the transparent balloon intact.
This was a fun demo put on by the local science centre. I suppose you could use a fresnel lens to focus sunlight down, but a) that's cheating and b) that works by a different method (the hot spot is only at the focal point).
Do do this demo, mount a speaker and a microphone next to a target. For best results, use a directional mic and the mic/target line at right angles to the speaker/target line (i.e. pick up sound from the target, not the speaker). Place an object prone to vibration (like a wine glass or other drinking glass) in the target zone, turn on your amp, and tap the glass's rim. It will shatter very shortly.
Get a glass or plastic tube, fill it a third full of water, seal the ends in a way that's waterproof, and lay it on its side. Put a speaker at one end, and hook up a signal generator to an amp to feed the speaker. Feed it with a sine wave and vary the range from about 1-10 kHz. When the frequency matches one of the resonant frequencies of the air channel in the tube, water "walls" will form at the antinodes due to the pressure vibration at the nodes exerts on the surface of the water.
I suppose if you turned the power up sufficiently you could get the same thing happening in a tilted or even vertical tube, but this would get quite loud and possibly dangerous (if you hit a resonant frequency of part of your support frame, vibration could damage a tube made of glass).
Fill beakers or glasses with coloured water (or kool-aid), and then either drop in a pellet of dry ice or pour on a couple of teaspoons of liquid nitrogen. Both will sit on a vapour cushion on top of the water for quite a while, and the cold will make dense fog on top of the water. Instant mist-boiling potion.
If you decide to drink this, use dry ice instead of liquid nitrogen, and blow out when you sip so the pellet drifts away from you. Better yet, don't drink from it at all. Frostbite isn't fun.
This is a fun and safe demo, but needs to be done in a fume hood due to fumes and sparks. Set up a retort stand holding two or three small cans. Cut the tops off of the cans, and fill them half full of sand. Line up the cans over each other, and put a patio stone or similar large flat slab of stone or concrete under the retort. Put a large can filled with sand on top of the stone, under the bottommost can. Over the topmost can put a ring stand with a piece of steel mesh you don't mind losing. Put a piece of paper or tissue on top of this, and put a small pile of thermite powder on the paper. Put on a leather gauntlet, and use a firework sparkler to touch off the thermite (ignition temperature is higher than an ordinary flame provides, a burner flame may detonate the pile, and a sparkler is safer than a powder trail of something easier to ignite). Optionally, put a small amount of something more sensitive on top of the thermite and light that with a burning wooden splint, but a sparkler is both simpler and safer.
NOTE: Do this with the fume hood down most of the way, and for safest results put a blast shield in front of the retort stand. There will be many, many sparks thrown by this demo.
The thermite will burn very brightly yellow-white, and will throw sparks everywhere and give off vapours (probably either water from the paper, or boiling iron oxide that wasn't consumed; I haven't checked). The thermite will burn the paper almost instantly, dumping white-hot molten iron through the rapidly disintegrating screen, through the sand in each can, through the bottom of each can, and down to the large can of sand at the bottom of the retort stand. It may eat through the bottom of this, but at worst will just slightly etch the stone (the stone won't react catastrophically with molten iron, and has enough heat capacity that you certainly won't melt through it and is thick enough that it won't crack through from heat shock).
This demo is quite safe, with proper precautions, and very impressive.
Lastly, things not to do. This is not an exhaustive list:
If done right, this can be safe, as water boiling off your hand forms a vapour cushion briefly. This is easy to screw up, and has drastic consequences if anything goes wrong. Don't do it.
This can also be done safely if done right, for the same reason - the dry ice or liquid nitrogen boils, forming an insulating vapour cushion. Briefly. If you hold it too long, or are just unlucky, you get a very painful and inconvenient case of frostbite, or worse. Don't do this.
I've heard of people drinking small amounts of liquid nitrogen. This is beyond stupid.
Protective gear is a must too, but even without it, a spark or a splash will only hurt _you_. Hurting your audience must be avoided at all costs.
Have fun.
Re:Cool demos I've seen. (Score:5, Funny)
In high school we had lots of explosions in physics class. Only one was unintentional. The teacher was demonstrating Ohm's law hooked a tungsten wire to a car battery. It glowed red hot. He then added two more wires (nine times the power) in parallel and the wires glowed white hot and then turned to liquid and dropped onto the battery. Seeing the fire, one of the kids yelled, "She's gonna blow" as a joke, but it seemed likely so many of us covered our faces. The battery exploded at that moment. I was on the front row and didn't notice any ill effects. The next day my pants came out of the washer missing the entire front of them. My shirt was in a similar condition. The chalkboard in the classroom was white except for the outline of the teacher's profile. You could see that he held his arms up to cover his face.
Re:Cool demos I've seen. (Score:4, Funny)
Wow. Just like what happens to the coyote in "Road Runner".
Kelvin Water Drop Experiment (Score:4, Informative)
A google search on "Kelvin Water Drop Experiment" gives lots of additional info.
Microwaves, Marshmallows & Light speed (Score:4, Interesting)
1) Get an older microwave. In particular, one without a turntable.
2) Get a microwavable tray as big as possible that will still fit inside the microwave.
3) Fill the microwave with miniature marshmallows.
4) Run the microwave long enough for some of the marshmallows to brown.
5) Measure the distance between the dark mashmallow bands, and convert to meters.
6) Multiply this distance by 2 (or 4?), and then by the microwave frequency, which should be listed on the back of the microwave.
7) If my instructions are correct, you should get a number awfully close to the speed of light.
What I've been told is that the microwaves can form a standing wave. The distance between dark marshmallow bands should be the wavelength, which when multiplied by the frequency, should give you the speed of light. (c = f*w).
Boiling water 'til it freezes! (Score:3, Interesting)
One cup of water in a vacuum chanber. Pump out the atmosphere. Water boils until only the low energy water is left, which then freezes.
Re:Boiling water 'til it freezes! (Score:5, Funny)
One cup of water in a vacuum chanber. Pump out the atmosphere. Water boils until only the low energy water is left, which then freezes.
Gee, you really went in a different direction in the second paragraph from where I thought you were going in the first.
Re:Boiling water 'til it freezes! (Score:3, Insightful)
lalala
15 seconds...
raining baloons (Score:5, Interesting)
it was cool at the time i swear
Re:raining baloons (Score:3, Informative)
Also, remember that H2O expands something like 500+ times in volume when turning into a gas. That would have had to be one helluva balloon to make a "crapload" of water.
Re:raining baloons (Score:4, Funny)
Also, remember that H2O expands something like 500+ times in volume when turning into a gas. That would have had to be one helluva balloon to make a "crapload" of water. I don't question his memory... I think his teacher activated the emergency sprinkler system...
From the Article on Leidenfrost effect. (Score:3, Funny)
"I have long argued that degree-granting programs should employ ''fire-walking'' as a last exam. The chairperson of the program should wait on the far side of a bed of red-hot coals while a degree candidate is forced to walk over the coals. If the candidate's belief in physics is strong
enough that the feet are left undamaged, the chairperson hands the candidate a graduation certificate. The test would be more revealing than traditional final exams."
I'm all for it! This will show whether they really believe in the scientific method in their guts.
(Fortunately I completed my undergrad in May)
Dangers of liquid nitrogen (Score:5, Funny)
RPI Physics Department Magic Show (Score:5, Interesting)
Make liquid oxygen by passing air through a coil of copper tubing immersed in a bath of liquid nitrogen (oxygen boils at a higher temperature than nitrogen). Great care is needed in working with LOX, it makes the damnest things catch fire!!!
Dip a cotton ball on the end of the proverbial 10 foot pole into liquid oxygen, wave it over a safely-distant flame, and create a BIG orange fireball.
Demonstrate that liquid oxygen is paramagnetic (weakly attracted to magnetic fields) by taking a BIG electromagnet with a small gap, placing a small test tube of LOX below the gap, firing a high DC current through the magnet, and video-watching the LOX being sucked up into the magnet gap.
With thanks to the late Professor Harry Meiners, otherwise a difficult person to work with, but a great showman...
triple point of water (Score:4, Interesting)
big sip, then stick it under a glass dome and crank down the pressure
until you can get it to a nice rolling boil without melting the ice.
You can impress people of all ages with that one. The trouble will
be in convincing them it's science, as opposed to magic.
Alumin(i)um and Iodine volcano (Score:3, Informative)
Make a dry mix of pulverised Aluminium and Iodine.
Then pour a small cone of the mix onto a fireproof base (my chem teacher used an asbestos sheet, but I'm not sure if asbestos is used in schools any longer). Make a small well in the top of the cone. The mixture is stable, right?
Well, watch what happens to the mixture when you put a single drop of water in the well. You get a plume of purple smoke and a handful of sparks.
The real question to ask the kids is "Why didn't the reaction begin until the water was added?".
IIRC, it goes something like this:
When Iodine dissolves in water, some of it hydrolyses into an acid (hydroiodic?) which reduces the oxide film on some the aluminium, leaving bare elemental Aluminium in contact with water, oxidising it. The heat from the water oxidising the Aluminium sublimes the Iodine, creating the purple plumes and melts more Aluminium leaving bare Aluminium in contact with oxygen in the air, starting the main reaction.
You might want to use a fume hood, though, gaseous Iodine is a little unpleasant.
Surprising Demo (Score:3, Interesting)
-Sean
Burning Mg strips in dry ice (Score:3, Interesting)
My favorites (Score:3, Interesting)
Another one I like is the burning carbon disulfide demo. I've seen this done using a long glass tube full of carbon disulfide gas. Drop a glowing splint in one end of the tube, and as it falls you get an amazing blue flame. Here's a link (hope you speak a little German) CS2 [cci.ethz.ch]
They did it a bit differently. As you might guess, this lab is a bit more hazardous and you do get some stink from the sulfur. It's pretty though.
Making your own mirror is another great demo. You prepare a small batch of silvering solution. ISTR using silver nitrate and nitric acid, maybe using an aldehyde as a reducing agent. I'll try to link to a recipe. Anyway, you mix the solution in a round bottom flask and begin swiriling. It takes about a minute, but as you swirl a silver mirror plates out onto the glass. Tollens Mirror [indiana.edu]
I used a bit of a different procedure, but this looks like it should work. You may consider keeping the flasks a little on the warm side (100-120 F) just before you do the demo. I've gotten better results compared to using cold glassware.
A great set of books is Tested Chemical Demonstrations, Vol. 1-4, by B. Shakishiri (University of Wisconsin Press.)
Mosbauer Effect is the Most Surprising I've Seen (Score:3, Interesting)
The demonstration at the equator, as shown on BBC, that demonstrates how the direction of rotation of water going down a drain reverses on account of moving a couple of hundred feet across the line was also amazing. But it was not genuine. It's bunko artists who are quite skilled. Lots of experiments like that one.
A torsion pendulum that can demonstrate the gravitational force from movable masses would also be a great demo.
Are these demos effective? (Score:5, Insightful)
How do you get people enthused about the actual process of science - coming up with hypotheses, figuring out how to test them, analysing the results, and so on?
Bed of nails, firewalking, (Score:4, Interesting)
I'd say: get a bed of nails. The bed of nails is probably the demo that hurts the most of the things I do, but it is not dangerous. It doesn't hurt just lying there, but then you put some brick s on you chest, and you get someone in the audience to break them with a sledgehammer. But it looks absolutely astonishing.
Check out David Willey's homepage [pitt.edu]. There's not much info on how to do things, but he does all kinds of weird things, and he's the guy who organized these firewalking record events.
Re:Burning money... (Score:3, Interesting)
Re:A good old classic. (Score:2)
Racquet balls work very well. Start the demonstration with them: start playing with a normal one. Someone takes it, dunks it in LN2, and starts playing again...
>>I wouldn't try the hand-in-boiling-lead anytime soon. Back when I was a kid, I made figures out of lead and I got some nice burns because of that. Lead splatting on your hands is not fun, and the Leidenfrost experiment didn't really help.
It's one of those "very impressive if you can do it but very dangerous if you can't" experiments.
Re:Air Pressure (Score:5, Interesting)
It's actually called "ooblech," not "gooblech," but what you're talking about is what you call a "non-Newtonian fluid." Technically, a non-Newtonian fluid is one whose viscosity is not constant for all shear rates. There are two types of non-Newtonian fluids: rheopectic and thixotropic. The viscosity of rheopectic fluids increases with increasing force; in other words, the harder you smack them, the stiffer they get. Thixotropic fluids are the opposite; their viscosity decreases as the amount of force applied increases.
If you read much science fiction, you'll inevitably run across the idea of liquid armor, sometimes called "armorgel" in the books. The basic premise is that you could cover vulnerable parts of your body-- like your torso, or your elbows-- with a garment that incorporates pockets filled with rheopectic fluid. As you move around, it feels like these little pockets have water in them, but when something dramatic happens-- like getting shot, or cracking your elbow on the tarmac-- the fluid hardens to absorb some of the force and to protect you. It's a fairly common idea, and one that's not totally far-fetched.
The suspension of cornstarch in water forms a rheopectic fluid. It looks and acts like a liquid when it's inert, but when subjected to force, it changes is viscosity pretty dramatically. For example, you can take a handful of cornstarch-water liquid and pass it from hand to hand rapidly. While you're doing it, it feels like it has the approximate consistency of silly putty or bread dough. As soon as you stop moving it, the viscosity drops drastically and it runs through your fingers.
Another fun demonstration is to take a moderate amount of cornstarch-water suspension-- say, 500 ml or so-- and pour it from a height of about five feet onto a tile floor. The fluid will pour like water, but when it hits the floor, it'll bounce like dough or putty. After a bounce, or two if you're really lucky, the mass will return to its liquid state and go all puddly.
Thixotropic fluids are more common and less interesting, because they're very thick when at rest, but grow thinner when subjected to force. The most common thixotropic fluid is ordinary tomato ketchup.
Another 2L pop bottle variant (Score:3)
If you get the fuel-air mixture right (this may take some practise) the rocket will launch itself a good 10 feet or so vertically, maybe 20 or 30 foot range if launched at an angle.
I've never seen one of these burst (those bottles ought to hold over 100 psi), but you never know -- you might have a defective bottle. And you are playing with fire. Beware bursting and fire hazards.
(Or, in the words of the motto of the Denver Mad Scientists Club [dmsc.org], "sumus scientes, noli hic domi temptare" (we're scientists, don't try this at home).)
Re:Best Demo Ever * THERMITE * (Score:3, Informative)
It's dark purple, and is rather impressive when mixed [wisc.edu] with glycerin...
Re:If he keeps taking these sort of risks... (Score:3, Funny)