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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.
Anything that explodes is cool. Baking soda and vinegar, Sodium and water, Magnesium and fire, drano and tinfoil... :)
put a little wax in a foil dish, heat it over an Bunsen burner, then squirt water at it... HUGE fireball... People don't think it will happen, but it does, it also seems to be safer than oil
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.
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
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!
The University of Wisconsin has a site at http://genchem.chem.wisc.edu/demonstrations/ that contains links to dozens of demos (with raitings) for various categories. I'm sure there is something for each age/interest level there
I would suggest the use of a microwave oven and a variety of things, my favorites are:
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.
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.)
Find free books.
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.
Yet Another Web Site
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.
If you were to release the cinder block with the flat side facing you and the rope attached in the middle, were it to turn in mid-swing and come back with at a 45 degree angle to the release position it would most surely split the skin from hairline to eyebrow.
- 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.
Immunix: Security Hardened Linux Distribution
Available for purchase
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
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.
A stream of water is split in two using a tubing "tee". Each stream then is allowed to drop through a bottomless can and into a catching can. The pairs of cans are crosswired and well-insulated. With the water streams breaking up into droplets as they pass through the bottomless cans, an initially slight imbalance of charge is amplified until a spark jumps between them. Typically a 1" spark can be attained after flow of 30 seconds or so. As the charge grows, the water dropplets of each stream repel each other providing an indication of the voltage buildup. If the weather is humid or the insulation of the cans inadequate, the charge leaks away without jumping the gap.
A google search on "Kelvin Water Drop Experiment" gives lots of additional info.
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.
This demo (which works very well) shows conservation of momentum. The tennis ball or basketball bounced alone will hit the floor with velocity V relative to the floor and rebound with velocity -V relative to the floor. When you drop the tennisball/basketball combo, the basketball hits the floor first, rebounding with velocity -V as before. The tennis ball, which is still moving downwards, then immediately collides with it at a relative velocity of 2V. The tennis ball rebounds with velocity -2V relative to the basketball, which is itself moving upwards at velocity -V, so the tennis ball moves upwards at -3V relative to the ground. Since the height attained goes as the square of the velocity (kinetic energy going like velocity squared and potential energy change due to gravity being linear in the distance ascended) the tennis ball travels nine times higher.
:-).
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
Curtains for windows?
My favourite experiment was when my chemistry teacher was introducing us to liquid nitrogen. As he was talking he had a large thermos of the stuff sitting on the table. He put on his lab gloves as he was talking, and then put his had into the thermos with his first finger dipped into the nitrogen. When he got the part where he was explaining how objects soaked in nitrogen turn brittle, he pulled his hand out of the thermos, and smacked his first finger against the edge of the counter. The collective gasp from the students when his finger shattered was followed by total silence (or was there some screaming too?). What he has done is "loaded" the glove with a piece of sausage in the finger of the glove - when he had his hand in the nitrogen, it was safely curled up in a fist! Needless to say, the demonstration was effective, and we were all very carefull when handling liquid nitrogen.
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.
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.
Gee, you really went in a different direction in the second paragraph from where I thought you were going in the first.
You haven't lived till you created plasma balls by shorting an AT power supply that was between your legs at the time. (this wasn't the intended goal)
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 :)
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?
Any sufficiently advanced technology is indistinguishable from a rigged demo
--Andy Finkel (J. Klass?)
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
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.
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.
Employee of Inrupt, Project Release Manager and Community Manager for Solid