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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.
I always had fun loading hydrocloric acid into a supersoaker-100 when I was a kid. You can buy it at any pool store. I could make nice messages in people's lawns with it.
Boy did I confuse the hell out of me ex-girlfriend when I wrote "I'm a dyke" in 15 foot letters into her lawn. She wondered how I did it since it was written in such nice cursive. I denied everything of course since her dad would beat the sh*t out of me. Its also fun to shoot at metal objects with it. I rusted a stop sign and broke off the pole in just 3 minutes. I had my supersoaker pumped high and I shot it with alot of pressure. The poisionous gas clouds that mist outward from the gun kind of suck though. Yes it can sting and burn your lungs.
I am glad I matured beyond this. However if I lived in Redmond Washington, I would probably still have alot of fun doing this.
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~A'Ëq'i4d)^'$ÊSÈòB
Although you don't quite qualify for the darwin awards...
Oh, come on, isn't there some kind of Darwin Honorable Mention that we can give him? Lord knows he deserves it....
I write in my journal
>>3: Pouring liquid nitrogen on your hand (the back, not your cupped hand)
This would dovetail nicely with the molten lead demonstration.
And, in all likelihood, you could wrap up the session with the ever-popular "trip to the emergency room" demonstration.
I write in my journal
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.
My hs physics teacher was fond of his suspended bowling ball and used it in numerous demonstrations--all very well and good until the support breaks and the ball flies into an unsuspecting student.
Moral of the story--Flying bowling balls have a considerable amount of momentum, and they hurt.
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.
In high school we had lots of explosions in physics class. Only one was unintentional. The teacher was demonstrating Ohm's law hooked a tungsten wire to a car battery. It glowed red hot. He then added two more wires (nine times the power) in parallel and the wires glowed white hot and then turned to liquid and dropped onto the battery. Seeing the fire, one of the kids yelled, "She's gonna blow" as a joke, but it seemed likely so many of us covered our faces. The battery exploded at that moment. I was on the front row and didn't notice any ill effects. The next day my pants came out of the washer missing the entire front of them. My shirt was in a similar condition. The chalkboard in the classroom was white except for the outline of the teacher's profile. You could see that he held his arms up to cover his face.
Lasers Controlled Games!
The chalkboard in the classroom was white except for the outline of the teacher's profile. You could see that he held his arms up to cover his face.
Wow. Just like what happens to the coyote in "Road Runner".
"Backups are for wimps. Real men upload their data to an FTP site and have everyone else mirror it." -- Linus Torvalds
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 :)
I do believe you're remembering this incorrectly. Yes, H20 will be the result of burning H2 and O2, but it'll be in the form of water vapor, not a liquid.
Also, remember that H2O expands something like 500+ times in volume when turning into a gas. That would have had to be one helluva balloon to make a "crapload" of water. I don't question his memory... I think his teacher activated the emergency sprinkler system...
Who moderates the meta-moderators?
Oh, come on, isn't there some kind of Darwin Honorable Mention that we can give him? Lord knows he deserves it....
Yes, I have a big yellow pin-on button for him that says "Me Stupid".
Table-ized A.I.