Reddit, what cool, easy DIY science demos do you recommend? So far my son and I have tried (1) microwaving a lit match and (2) submerging a hot empty aluminum can upside-down into cold water. [Both are very cool, and both I found on Reddit.] What other relatively easy science experiments you like?

I've lurked on Reddit since before it had a mock rivalry with Digg, but your post forced me to register.

For background, I'm months from getting my Ph.D. in physical chemistry, so I'll be mostly familiar with chemistry/physics ideas. Sadly, many of the great chemicals that used to be available in a home chemistry set are now restricted. Still, The Golden Age of Chemistry:

http://chemistry.about.com/b/2007/12/07/the-golden-book-of-chemistry-experiments.htm

isn't a bad place to get ideas from. The book as a pdf is linked to on that page.

There are many simple physics experiments that make an impression. Pressure and several related concepts can be taught from your aluminum can experiment. Boiling a little water in a coffee can or similar item with a tightly sealing metal lid can result in spectacular but safe implosions. In fact, you can do one at room temp and a second in an ice bath to discuss rates of cooling.

You can tie a jump rope to something and wiggle it to create standing waves.

I don't own it, but the recently published "The Dangerous Book for Boys" would be another good resource. I've seen several glowing reviews.

Try calling the local university chem department and see if you can get some liquid nitrogen. It's cheaper than milk for departmental use where I'm at. A container will be hard to find, but you might be able to try a few things on site, or beg a dewar. Ping pong balls, plants, just about anything acts weird when cooled that far. It even "dances" over surfaces because it floats upon a self provided air layer.

Sugar and salt crystal formation from evaporation is simple, and the crystals are different formations. I know that simple NaCl has a square packing system, but I don't recall sugar. Should be easy to google.

Food coloring in hot and cold water serves for a measure of diffusion, plus it shows off internal currents. Liquids at rest have a surprising amount of motion going on.

Food coloring + white flowers in a vase = colored flowers. You can even observe the petals change overtime.

You can measure the amount of water in food by weighing it (scales are cheap. dealextreme.com is a GREAT supplier of Chinese produced junk. shipping is free but slow) then dehydrating it.

Baking soda plus vinegar is an oldie but goodie. Lots of chemistry concepts there. Acid/base reaction, gas formation, etc. It's probably energetic enough to measure a temp change in water with a thermometer. Capture the produced CO2 and putout a match with it.

Speaking of water, intermolecular forces are pretty strong. You can demonstrate this by filling a container past the top without it spilling over (to a point of course). The water also creeps up the sides of a glass surface because it's fairly attracted to said surface. Hydrophobic and hydrophyillic surfaces will casue water to bead and spread out respectively.

Diffraction of light with a laser pointer should be possible. A double hole or double slit experiment would probably work. You also might be able to show light waves interfering with one another by passing a laser through a piece of glass, and slowly adjusting the angle of the glass. The reflections off the front and rear surface will interfere. This is really easy to do, but you'll need steady mounts. A similar observation can be made with two pieces of glass (optical flats) placed on one another. The imperfections create one hell of an interference pattern. The changing fringes of the glass reflections lets you measure how much more glass you've added to the path length. If you want, I can walk you through the equations 10 hours from now.

The Journal of Chemical Education requires a subscription to access online, but most university IP addresses would work. It might be a bit advanced, but they have a "chemistry for everyone" section that might help with ideas.

You can make charcoal with wood in a sealed test tube over a flame.

You could build a Faraday cage around a radio. Aluminum foil or chicken wire should work.

Sorry about the stream of consciousness. I need some sleep. Enjoy showing your son the wonders of our universe.

Oh, a stunning amount of basic astronomy can be greatly improved with a set of binoculars. Optics planet had refurbished Nikon Action Extremes ones for a great price 2 weeks ago. They get small enough for a child to use with both eyes, and the 8x40 ones won't be too heavy. They also have a cheaper, but not as nice "action" line. A $20 adapter for a tripod + cheap tripod makes for a great platform for holding things steady during lunar and stellar observations.

Best of luck.

2nd edit. Tuning forks!

Get three tuning forks. Two of the same frequency, one different. Hold one of the pair,and give the other to your son. Hit yours, wait a few seconds, then stop it. Your son's will now be "on" This is because the sound waves produced by your fork drive the second at its resonance frequency. If you strike the forks set at different frequencies, you'll hear them beat against each other as the sound waves constructively and destructively interfere (like a pond with tow rocks thrown into it). You can probably buy/ borrow two identical tuning forks, and add a small magnet to one to change the frequency. Play with how far out to place it to get a good effect. Err, have your son do that. You can probably also show off the Doppler effect with one as well.

I've always liked the non-Newtonian fluids experiment.

http://www.exploratorium.edu/science_explorer/ooze.html

• cut a red grape in half.

• place it end to end where the stem hole is. the two halves of the stem hole need to be touching.

• microwave until flames happen

demonstrate an estimate for the speed of light!

materials: chocolate bar, microwave, ruler

put a chocolate bar horizontal in a non-rotating microwave and microwave on lowest setting (defrost maybe) for a couple of seconds until you see molten globs start to form. stop microwaving. take chocolate bar out and measure distance of globs.

Glob distance should be 2x wavelength in centimeters for the radiation in your microwave.

microwave frequency should be on the back of your microwave.

use C=freq*wavelength to find speed of light! (my microwave showed c=2.93x10⁸ m/s)

Find a wine cork. Cut it in half long way. On the curved side stick 3 evenly placed wood matches head up in the cork. Get a small plate that has a lip on so it will hold water. Place water in the plate. Set the flat side of the cork in the water your little match craft should float. Now light all the matches and quickly place a tall cup over the cork. You will create a vacuum that will suck the water up into the cup.

mentos and coke would be fun for a kid.

my personal favorite: the electric pickle

• take an old extension cord.

• strip and split the female end (heh)

• connect the exposed wire, one each, to 2 metal forks

• stab the forks into each end of a dill pickle.

• plug the cord into the wall (and turn out the lights for full effect).

one end of the pickle will light up...it will continue to stay lit until the fork times are fully coated in carbon.

note: this a good way to ruin a fork, stink up your house, and probably shock yourself. a bit dangerous but i like it.

might not be appropriate for a kid but i learned it from Mr. Wizard.

Upvotes all around! Thanks, everyone! I can't wait to try your ideas.

Dude

Wholly Irresponsible Experiments is an awesome book.

http://www.amazon.com/Wholly-Irresponsible-Experiments-Sean-Connolly/dp/1840468122/ref=sr_1_2?ie=UTF8&s=books&qid=1240295719&sr=8-2

make a pendulum with something large and heavy. let it swing away from your nose and towards it again. let your kid try, too.

Fill a glass with water up to the rim. Put a piece of cardboard on it. Turn the glass upside down and explain why the cardboard stays in place and keeps the glass sealed.

Steve Spangler is pretty cool and I've always loved dry ice, so here's a cool experiment from his site: http://www.stevespanglerscience.com/experiment/00000055