Slashdot Mirror
Surprising Science Demonstrations?
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.
Get some milk, some cream, some sugar, some vanilla, and any other candies you may want to add, mix it with LN2 until it's frozen, and eat!!! "Steams" a lot (the steam is actually frozen water vapor). Directions here Yum!
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....
"A language that doesn't affect the way you think about programming, is not worth knowing" - Alan Perlis
Many years ago, I did a couple of science programs as part of a science after-school program at a downtown middle school.
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.
[Insert pithy quote here]
I suspect that what you saw was a bill doused in off-the-shelf rubbing alcohol, which is basically methanol diluted with water. Soak the bill and light it; the alcohol will burn off, and the water remaining behind will keep the bill cool enough to avoid charring. A distantly related demo involves boiling water in a paper cup over a fierce fire... it's most dramatic in a roaring fireplace, but a bunsen burner ought to be good for a laugh, too. The water keeps the paper cup cool enough (100 C, of course) to avoid burning.
--Larry
Never attribute to malice that which is adequately explained by incompetence
Take a tennis ball and a basketball. Bounce each separately in front of the kids. The place the tennis ball on top of the basketball and drop both. If you do it right, so the two are in contact when the basketball hits the floor, it will definitely shock them. The basketball will hardly bounce as its kinetic energy is transfered to the tennis ball. The tennis ball will shoot up into the air as if fired from a cannon! Be sure to have lots of head room for this one.
Back in college we (the Society of Physics Students) would have a demonstration of stupid physics tricks. Try some:
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...
Life is short: void the warranty.
Also, try goobleck. It's a cornstarch based substance that behaves as a solid or a liquid. Water is the other ingredient, but I don't remember the ratio.
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.
I write in my journal
My kids (6) were fascinated with this science project.
:-/ "[Cough] Do you have some Binaca?")
We also tried the Binaca cannon. (The kids also went nuts with Ace Ventura jokes
And, yes, my homeowner's insurance is rather pricey...
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.
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... :)
The birthday paradox is suprising. It is a good example of how bad humans are at calculating probabilities.
:-)
Ask everybody in the workshop to shout out their birthday (day, not year) one at a time, and ask people to raise their hand if they have the same birthday. In a class of 30, the chance of a coincidence is 70% example, explaination.
There is a 50% chance that two people out of a group of 23 will share a birthday.
If noone shares a birthday you may look silly though
For the little piros-in-the-making, you could do as we did (as kids). Tightly wrap one layer of tin foil around the head of a match, being careful not to cover more than the phosphorous material (but no need to be anal about it, either).
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.
I haven't confirmed this one myself, but if it works, it's pretty cool.
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).
"You know, Hobbes, some days even my lucky rocketship underpants don't help" -- Calvin
The most impressive physics demo I've ever seen was with a motor gyroscope. It's quite small in size but it's got a low friction very dense heavy rotor inside (about 10 lbs) which can spin up to very high rpms. It's got two convinient handles along its axis. It is first connected to the outlet and is spun. After it's spining rapidly you cannot change the direction of its axis even when you pick it up in the air and even with two people trying. It's spooky. Imagine picking up a small 10lbs dumbbell and not being able to turn in any way with some invisible force preventing you whichever way you push it!
This one required quite a bit of work, but you have it forever once you've done it ...
... you die ..."
Make a bed of nails. Probably 50x150, with nails every half-inch or so on a backing of double-thick plywood. You set the stage by taking off your shirt, so it's guaranteed to get attention. Then you simply lay down. This demonstrates how mass can be distributed in a way that no one nail is supporting enough weight to break skin.
My physics teacher in high school did this one, and it has stuck with me lo these many years later.
When he was showing us formulas and equations and such, he always couched them in terms of a person in peril -- standing at the top of a cliff, being whirled around by angular momentum or whatever. The solution to the equation was always accompanied by "And then
All of these lessons have stuck with me far better than my junior-year chemistry lessons, for which the teacher left the class to make soup (don't ask) and drink liquor in the lab and told us to learn it from the book.
This is one of my alltime favorites. I've been thinking about getting a vacuum pump so that I can do it in the comfort of my own home.
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.
See the photos here!
it was cool at the time i swear
I want 2D games back.
Magnesium and fire, drano and tinfoil... :)
;-)
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
If you don't understand any of my sayings, come to me in private and I shall take you in my German mouth.
OK, when I was in maybe 10th grade, I went to some sort of statewide science symposium. Of course, the first night, we had a professor give a talk that included a lot of exactly these sorts of graphic examples of chemistry and physics for entertainment.
The big show stopper at the end of his lecture was amazing. There was some sort of chemical reaction - I have no memory of the reaction whatsoever, but he went through it fully on the blackboard beforehand. It had a metal reaction chamber, manufactured such that it made a quiet whistle as the reaction went on - must have been the evolution of gases. Perhaps there was some sort of glow or light as well. He asked that everybody (hundreds of us in the lecture hall) be very quiet, and they turned off the lights as well. At first not much happened, then it started to whistle, and got quieter and quieter. Everybody is sitting in suspense - you could hear a pin drop other than the whistle.
When the whistle was almost inaudible (which meant that the reaction had run to completion) there was some other combination that occurred. With the result of an incredibly, mind-shatteringly loud and unexpected BANG accompanied by a powerful flash of light. I clearly remember seeing the professor's grinning face in the flash.
Whatever it was, it was great. Didn't convince me to be a chemist, but surely made me think about it.
Anybody know what this was? It seems like this might have been something that was separating hydrogen and oxygen from water, then explosively recombining. Or perhaps it was something about activation energy - the original solution decomposes into stable components until the original material isn't present anymore, then the temp climbs and kapow!
David Fung
It might open one or two students' minds to some of the notions of finite math and calculus, which would be a bonus. Plenty of opportunities to use a simple spreadsheet model to calculate the kinetic energy from the final stage.
Most students would benefit from a practical analysis of Newton's Laws of Motion, and this is an excellent opportunity to relate mathematics to the visceral impact of ball bearings shooting through 2x4's.
Don't forget to film it for later analysis and instant replays, as you probably don't want to be shooting high-velocity projectiles in close proximity to the students very often.
Back in the 1980's, when I was a Physics grad student at Rensselaer Polytechnic Instutute in Troy, NY, there was a tradition of putting on physics "Magic Shows" for the freshman classes. A few dramatic classics included these:
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...
"My strength is as the strength of ten men, for I am wired to the eyeballs on espresso."
1) Take a newer U.S. Penny, make a small notch on the edge of it with a blade, place in sulfuric acid. (Newer penny's are made of zinc, plated with copper... after about 10 or 15 minutes, the result is a paper-thin shell of copper shaped like a penny, almost like tin-foil.)
2) Get an empty #10 can with a plastic lid (such as a coffee can). Punch a hole in the side, about 1/3 to half way up - the hole should be just big enough to fit in the end of a rubber hose (such as a bunson-burner hose). Pack some ordinary all-purpose flour into the hose. Stick the end of the hose in (about 18-24 inches long - with the flower at the end in the can), and seal around it. Place a burning candle into the can. Demonstrate that you cannot ignite a pile of flower, then place the lid on the can, and blow on the hose - BOOM!
Draw some tap water into a large beaker with some ice cubes, take a
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.
Cut that out, or I will ship you to Norilsk in a box.
When I was a little child in grammer school .25 gallons of
we conducted this experiment:
Fill a clean 1 gallon gas can with
water.DO NOT put the cap on yet. Place on stove and bring water to a boil.
With oven mittens, take the can off the stove, and
place in the sink. With oven mittens again, screw
the cap on. Pour cool water on the
can in the sink.
You have now proved the existence of atmospheric
pressure. As a child I remember being startled at this unexpected result.
We first lit some candles in small aluminum candle holders (cupcake baking foils) and watched the candle get smaller as it burned and saw the light coming out coming and felt the heat. So I formulated the hypothesis that wax must have a substance in it that is given off as heat when it burns. The candle gets smaller, the heat and light come off. Obvious.
So I suggested that we capture this stuff, lets call it phlogisten, a name I suggested that Priestley had used for the substance.
We could catch it in a jar by putting the candle in a the aluminum cupcake holders, floating the foil in water in a saucepan and putting a jar over it. As the phlogisten came out of the candle it would go into the air pushing the water down and so we could measure how much was given off.
Nice scientific experiment. Obvious hypthosesis, easy and cheap experiment, expected result. If you know the actual result, you have a wonderful way to show that one needs experiments as well as theory to further science.
For a physics seminar a while back I was required to present to a bunch of middle-schoolers a short bit on atomic clocks and laser cooling. I quickly realized that much of this stuff was way over their heads and, more importantly, outside their interests.
:) Good luck, buddy.
What did get them sitting up straight was a cylinder of liquid nitrogen I had ready to help me compare temperatures. (I had planned on showing just how cold cold can get.) Every time I spilled a bit on the floor they all screamed in delight. I ended up borrowing a few balloons from a fellow classmate who was presenting the same day and demonstrating instead the relationships of pressure, temperature, and volume.
My suggestions? Go with something fairly easy to understand (especially if you're planning on keeping the attention of a wide range of ages) and also fairly exciting. Oh, and don't be afraid to improvise.
Atttach a nozzle on the OUTPUT of a vacuum cleaner so it aims Upwards into the Air at a 45 degree angle, place a BEACH-BALL in the stream of out-blowing air about a foot away, and Watch It Just SUSPEND there - since the air moving around the ball creates LIFT enough to keep it up.
;-)
sorry about the AC post, but i'm away from my CPU, and forgot my password (having to remember umpteen gazillion passwords is a #%# pain!), so here's a URL to my site (which means its not actually an 'anonymous' post anymore...
best regards,
john
My science teacher in high school did this one that I really liked:
Heat up an empty pop can over boiling water (using tongs of some sort), right side up. Then, quickly turn it upside down and plunge it into an icewater bath. It will implode with a small pop and end up almost as small as if you had stomped on it to crush it for recycling.
Don't steal. The government hates competition.
Nothing was more surprising than our surprise demo on capacitors, where a 10,000 volt capacitor was charged by the prof and discharged onto an arc of aluminum foil. Boom.
-Sean
My high school physics teacher, once we got to the section on Newton's laws, did this every year...for real:
First he would take out a large 'Bed of Nails', a body length piece of wood with nails evenly spaced out over the wood with the pointy-sides faced upwards, and lay down on it. Then he would take another, smaller piece of wood with nails driven into it and put it on his chest, with the pointy-sides facing his chest. Then another teacher would come into the room, bringing in a **CINDER BLOCK** and put it directly on top of the nail-laden wood on top of the physics teacher's chest. Then the assistant would pull out a _Sledgehammer_ and give the cinderblock a hit with full force.
The cinderblock breaks, the physics teacher survives, and his shirt is only slightly imprinted with a grid of pointy impressions. The force of the sledgehammer's impact is completely absorbed by the cinderblock and not the teacher's body. If the cinderblock did NOT break, the teacher would receive a hundred holes in his body.
He did this every year and never received a wound. Amazing, really.
Salis
Favorite
other memorable demonstrations from 9th grade science class:
:) We tasted successively stronger acids until we got to hydrocloric acid, as I recall. I just got a slight whiff of that one, not a real good taste.
:)
put a feather in a vacuum chamber and watch it fall as fast as a rock.
fill a mason jar with pure oxygen, light a piece of steel wool (which will have a very feeble red glow where you lit it, if anything) and then put it in the pure oxygen. It lights up real good.
fill a mason jar with pure hydrogen and then open the jar and light it up. It just makes a big bang if memory serves.
(there are probably safety considerations with the last two which I'm forgetting.)
Someone already mentioned the gas can filled with boiling water which you seal and then cool it down to cause the gas can to be crushed by atmospheric pressure. That was another good one, from high school chemistry.
Also in high school chemistry we had an "acid tasting experiment" which I don't recommend you try.
There are a lot of good little science toys, I mean demonstrations, at Scientifics Online. The van de graaf generator is cool, of course. There is also a magnetic levitator which is very cool, but its scientific value is unclear.
Here's a cool (cold, actually) one: Buy 2 roughly 2lb blocks of dry ice. Scoop out a golf-ball sized hole in one of the blocks, and drop some magnesium shavings in. Ignite the shavings with a lighter/bunson burner/etc. Do not look directly at the burning Mg. It will hurt. But _do_ notice that it burns a bright white. Now put the second block of dry ice down on top of the first block so that it covers over your pit full of burning Mg strips. You'll notice that even though the Mg is now in an atmosphere of pure CO2, it continues to burn. And now it's a pretty (and much less painful) red color.
One of my favorites is the sodium acetate tower. It is a very safe demo that gets a good reaction out of just about any age group. You make a supersaturated solution of sodium acetate in a spotlessly clean beaker. Show everyone the clear liquid (looks like water) then start slowly pouring it on the table. Crystals of sodium acetate form as you pour, and the water is trapped within the crystals. You wind up with a pile of fairly dry looking sodium acetate and no liquid. Very impressive. Sodium Acetate Tower
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
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
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.)
Lasers are also fun. Cut a small hole low-down in the side of a clear (white, preferably) soda bottle. Fill the bottle with water (covering the hole!) and shine a laser through the bottle and onto the hole.
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.
Sigmentation fault - core dumped
Twirlip of the Mists is one of the posters on the galactic Net. He comes across as either being kind of a newbie, or as communicating in a language so far away from English as to make meaningful translation almost impossible. His big catchphrase is, "Hexapodia is the key insight," and he talks about what humans' having six legs means in the grand scheme of things.
;-)
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.
I write in my journal
One very easy and SAFE experiment is the one with an office chair and a bicyle tire.
Someone sits on the (rotating) chair and holds the tire in front of him. The tire is spun, and then the person sitting in the chair rotates the tire.
Result: The chair starts spinning.
If the person rotates the tire fast enough, he could fall, but othervise the experiment is pretty safe, no explosions or fire, but unexpected none the less...
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.
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. 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.
Employee of Inrupt, Project Release Manager and Community Manager for Solid
When I was studying chemistry I had fun with this. Sorry, I'm used to MKS system. Prepare 1 liter of solution containing: 10 grams of NaOH 10 grams of C6H12O6 (any of the 16 works, only changes speed) 1 drop of 1% solution of Methilene-Blue (well, I've never used a drop, but directly joined a couple of grains) Fill half a bottle and close it. Within a little time it seems clear water, since NaOH+C6H12O6 turns Methilene-Blue to a not-oxidized state, but as you shake the bottle, the Oxigen takes it to blue again, then it turns again clear... You can repeat it some times; open the bottle if it doesn't work anymore: maybe you've consumed all the Oxigen... Have fun!
hehe, my chem teacher used to call it 'negro penis', but he did it in a beaker about 3 inches in diameter, with alot of sugar and alot or h2so4. it would grow the whole period, to about 10 inches hight! if i remember correctly, the h2so4 has to be pretty pure (no/not much) h3o+.
Doc Staffan Andesson, does a theather of natural (physics) history. Quite effective. The audiance is in the story, learns a lot of science and history, while taking part of the story and experiments. Bombs and story is da thing.
There are some quicktime video clips: http://www.ambassaden.net/fysik/videoklipp/klipp1. html
and some streaming: http://www.ambassaden.net/fysik/kulturnatten2001/
Check out this group's (Lifters) web page for amazing experiments in what appears to be anti-gravity. There are simple and complex plans for others that wish to re-create these experiments.
http://jnaudin.free.fr/html/lifters.htm
This is not quite along the lines of violently hot or explosive materials, but it is quite surprising if you've never seen it: http://www.essex.ac.uk/psychology/visual/thatcher. html
If you've got baking soda and water, why not demonstrate the fire extingushing effects of CO2. Mix baking soda and vinegar in a tall glass, only fill the glass about 1/3way with vinegar though. You want to pour the CO2 out of the glass and extinguish a candle, without pouring any vinegar out.
M@
Krispy Cream is people
When I was a cubscout leader, I stumbled on a cool idea used in a ceremony. Soak a cloth in a mixture of 40% acetone and 60% water (keeping it in a sealed jar so the acetone doesn't evaporate). Then you can light it on fire, and the evaporating acetone burns, but the cloth itself doesn't. A link to the details in the context of cubscouts is here
Yes, I agree. If I ask a hit man to kill you, but I don't pay him a penny, then I should get the punishment that is on the books for talking. See the problem with the kind of justice that is performed with a simple lookup table?
If tits were wings it'd be flying around.
This is an experiment I did in a chem class back in high school. My memory might be a bit fuzzy.
:)
Pennies are not all copper, but a thin copper 'shell' around another metal. With a small file, file a few (3 or so) notches in the sides of the penny so that the other metal is exposed. Place the filed penny in a beaker and cover with acid (I don't remember which acid, probably sulfuric). After a while the acid will have 'eaten' away the other metal, leaving only the copper shell. This shell (you did wash away all the acid, of course) looks indistinguishable from an ordinary penny. Watch the students' faces as you throw the penny into a glass of water and it floats - then pick it off the surface of the water and crunch it into a little ball with your mighty fingers
Caveat Emptor is not a business model.
Here are three experiments that I've seen/done that I've thought were very impressive.
1. Take an empty gallon paint can. Drill a 3/8" hole in the center of the lid, and in the side about 1/2" from the bottom. With the lid on, purge the inside with natural gas. Now set it on the floor and light the top hole. This will produce a steady flame 2 or 3" in height. Now you have to do some acting. Make it seem like something cool is going to happen and get the viewers to watch intently. After a minute or two they will start to get bored as all that will happen is the flame will slowly appear to die. After a certain point, tell the viewers that something went wrong with the expermient and you'll have to try again once the flame has died out. As time progresses, the flame will grow smaller and will actually disappear from sight as it drops below the hole. Fairly shortly after it does this, the ratio of oxygen to gas in the paint can will reach the appropriate mixture and will explode launching the lid of the paint can about 8 ft' straight up, and startling everyone who has forgotten abot it. Obviously, this needs to be done well away from the audience.
2. This requires two large bricks of dry ice (about 12" square, 4-5" thick), some magnesium shavings and a blowtorch. Take the bricks of dry ice, and hollow out a small area so that you can stack them trapping a small pocket. Put the magnesium shavings in the pocket, and light them with the torch. Put the other brick on top sealing the thing in. Because magnesium can use carbon dioxide as it's oxygen source, it will continue to burn inside the dry ice. It produces a really incredible glowing effect from the ice. After burning for a while, the glow will reduce and will actually begin to pulse.
3. Finally there's Peryoxyacetone (sp?). I don't remember exactly how to make it, but you can find it in Chemical Demonstrations: A Handbook for Teachers in Chemistry by B. Z. Shakashiri. The books are excellent as a whole, the the peryoxyacetone, is escpecially impressive. It's a white powder that burns in a nice big fireball. It burns quickly enough (and at a fairly low temperature) though that it can be used to demonstrate the leidenfrost effect. Placing a small pile on the open palm of your hand you can light it, which creates an impressive looking fireball that you can't even feel. I'd suggest trying this on a piece of paper the first time. If you've got the right stuff, there won't even be a scorch mark on the paper.
My favorite simple demo for elementary students is to build a two pan balance with a meter stick hung from the ceiling by thread. Hang a balloon (uninflated) at each end of the stick with thread and paperclips so that they balance. Then blow up on of the balloons, and take a vote of whether the inflated balloon will be lighter or heavier than the uninflated balloon. Everyone is always surprised by the outcome.
Tobacco companies engaged in a massive campaign of fraud and deceit. Are you claiming that firearms manufacturers have behaved similarly? Has any gun maker ever tried to cover up evidence about the deadly nature of gunshot wounds, for example?
Tom Swiss | the infamous tms | my blog
You cannot wash away blood with blood
And getting those warnings placed there was a volunatry action of big tobacco? Hell no. It took years, while the tobacco companies hid evidence, lied, and fought tooth and nail against any suggestion that smoking was unhealthy.
Handguns are made to throw lead pellets very fast. Those pellets may be thrown for recreation, for defense, or for assault.
The same reason crackheads have no problem acquiring rock: prohibition doesn't work.
Tom Swiss | the infamous tms | my blog
You cannot wash away blood with blood