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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!
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]
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.
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.
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
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.
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."
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.
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.
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