Plasma in a microwave (not entirely dissimilar to grapes sparking; link with science commentary). Light a candle in the microwave and cover with an inverted Pyrex containment vessel, partially resting on something to provide a small air space at the base. This should allow for a glowing ‘cloud’ of plasma to be maintained inside the jar. Don’t keep it running for very long, be aware that even Pyrex will fracture given sufficient time (as shown in the link), and switch the microwave off and leave to cool before opening the door or handling the Pyrex.
My high school Physics teacher had a good one. He set up a peashooter at the back of the classroom. At the top front of the room he hung a metal ball on an electromagnet. The switch to turn off the magnet was at the tip of the peashooter.
He would load up the shooter, aim it straight at the ball, shoot it, the switch would trip, the ball would fall and the pea would hit the ball.
It looks at first glance like an amazing piece of breath control but it’s just two objects falling at the same rate.
I recently discovered this guy, he’s got tons of cool science ideas that you can build at home.
I’m currently working on his little generator, but I want to make mine out of more permanent materials.
After that I don’t think I’ll be able to resist making my own poor mans ‘Liquid Nitrogen’
I’ve never had the honor of doing it myself, but a homemade cloud chamber would be aces for me.
That or a full-on Atomic Energy Kit™.
People today just have no guts.
I always loved the “suck an egg into a bottle” trick. ffffooomp!
I recall a demo in 8th grade science that was a contact explosive made by mixing ammonia and iodine. Pretty cool, but not something I would do now if I were an 8th grade science teacher.
Another crowd pleaser is the balloon filled with methane on a long string, a balloon filled with hydrogen on a medium-length string, and a balloon filled with nitrogen on a very short string, each held by a student, and ignited by the professor with a candle-on-a-stick in that order . . .
Cal
The fellow at leapsecond.org, who collects atomic clocks and operates a very accurate timekeeping system in his house as a hobby, describes taking an atomic clock along when camping on a mountaintop. Due to the relativistic effect of the higher altitude, this clock now disagrees with the other clocks that were left home for the duration. It is neat that one can manage to demonstrate this effect with involvement at the level of the hobbyist.
We went to school in parallel universes.
My chemistry teacher made contact explosives with potassium permanganate. And the exploding balloons were filled with hydrogen. He’d put zinc chips in a flask and add HCl. He’d put a balloon over the opening to the flask and fill it with the pure hydrogen. The ceiling in my school was made out of concrete…hard to explain, but it had sections that were like cubes with one side missing. The balloon would float into one of the sections and he’d ignite it with a candle on a yard stick. Sounded like a shotgun going off.
Here’s to you, Mr. Mattox!
That’s interesting, my 8th grade science teacher was a Mr. Maddox . . .
Huh? Did you actually see this clock? I remember hearing something about if you took a watch in to orbit for 30 years it would be off by something like a second. I’d be surprised if taking a clock on a mountain for a few days would make any kind of measurable difference.
Besides, don’t atomic clocks update themselves from time to time, isn’t that what makes them so accurate?
Well, we’ve either reinforced the parallel universe theory or you’ll think I’m a stalker 
I was in my chem teacher’s class in 10th grade. I suppose I’ll get pitted for acknowledging the existence of the stereotype of the coach who can’t teach and only shows movies (believe me…they exist…), but this guy was not that coach. He was freaking huge, and a football coach, and he was one of the best teachers I ever had. He was VERY strict and demanded strict attention with no talking in class, but he never once lost his temper or got angry. He told great stories and had a great sense of humor. He used “sciencey” props whenever he could. He taught me so much about chemistry and and how to balance equations, that three years later when I took chemistry in college, I never had to study…not even for the final.
Not sure what was my favorite…the contact explosives, the exploding hydrogen balloon, or…the sodium dropped in a bucket of water
I recall some stupid teenager who played around with this. It was all good fun till they nearly lost their eyesight.
My eyes are fine now, thanks for asking
If you visit the site linked, you’ll see the was off by a matter of nanoseconds- measurabley affected, but in a very small way.
Atomic clocks don’t update themselves- they’re just a measurement of the resonance frequency of an atom that happens to line up with our definition of a second, and the organization that runs the “official” atomic clock sometimes adds leap seconds if they find it necessary.
Huh, I didn’t even notice that was a link and somehow my brain read it as a teacher that was talking about this.
You should be aware that this isn’t considered a benign experiment any more – because
It also reacts pretty violently with many substances, and if heated. Even if it weren’t a suspected carcinogen it’d be a bad idea to play around with it.
Same thing’s been happening to a lot of the “classic” science experiments from when I was a kid.