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.

Comments

Hot Wax

[403Forbidden]

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.

Re:Hot Wax

[pyrote]

And if you wrap it a little further down the (paper) match and put an un-folded paperclip along the side, you form a micro sized rocket engine. Remove the paperclip before launch and you have the tube for the exhaust.
You can even make the paperclip into the launchpad.

Here is some other designs:
http://www.matchrockets.com/fire/mr.html - This one has Video and info on calculating velocity!

http://users.bigpond.net.au/mechtoys/matchrocket.h tml

http://www.grc.nasa.gov/WWW/K-12/TRC/Rockets/match _rocket.html

http://mrockets.hypermart.net/brett/

http://www.reachoutmichigan.org/funexperiments/age subject/lessons/other/match_rocket.html

some good ones

[cybercuzco]

Well, given unlimited access to equipment (as in your vat of molten lead example) Here are some good demos that ive personaly seen:

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

[cybercuzco]

Youre right, it isnt ferromagnetic, but when a large alternating current is applied to the solenoid, it induces a current in the aluminum, since its a good conductor. The current that is induced produces a magnetic field that is opposite to the one produced by the current in the wires. This rips the can apart in a very cool and explosive manner.

Collection of Chemistry Demos

[segfaultcoredump]

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

Re:Collection of Chemistry Demos

[bellings]

Another guy at the UW has a page up for a demo he gives each year called "The Wonder of Physics." I remember going to this thing once when I was 12 or 13, and being extremely impressed.

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...

Microwave of Course!

[coryboehne]

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.

Re:Microwave of Course!

[coryboehne]

Doh! I did'nt include a cool link in the above post... A great site with videos of most of the reactions is available at http://members.tripod.com/~hochwald/microwave/micr o.html And what ever you do, try these out first (some experiments can actually cause explosions or fumes) Probably outside experiments are the best, possibly even destroying the light in the microwave and doing them at night (should put on a good show) Of course the damage done to the magnetio is definately a factor, so be sure to have a spare handy, but with the price of microwaves (used) at around 20 bux, that should'nt be a big problem.

angular momentum; hands-on stuff

[bcrowell]

I always get a good reaction with angular momentum stuff. Spin a weighted bike wheel, sit down on a rotating stool, and flip it over. Ask two students to get on the stool and find some way to cooperate so that they can start rotating together. (They can't.) Spin the wheel and hang it from a rope so it precesses.

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.)

Here's a classic

[foistboinder]

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:Baking soda and vinegar

[p3d0]

I rusted a stop sign and broke off the pole in just 3 minutes.

Well, that's really nothing to boast about.

Other possible problem

[coryboehne]

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.

Flourescent Pickle

[Crispin Cowan]

Pickles flouresce (glow) when subjected to 120VAC. To demonstrate:

1. Get a lightweight, 2-prong extension cord.
2. Do not plug it in yet.
3. Bare the ends, and wrap them around two medium-large nails.
4. Insert the nails into the pickle.
5. With all hands off the pickle and the bare metal, plug in the cord.
6. 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

Kelvin Water Drop Experiment

[CraigV]

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.

No explosions

[KjetilK]

Well, I'm not so sure all the kids like things that explodes. Some may only be frightened, and they will forever think that science is only about destroying things. It is a real problem that many people think that.

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.