Explosions--you know, for kids!
May 16, 2017 8:23 AM   Subscribe

Our last Girl Scout meeting of the year is coming up next week and I think it'd be fun for the girls to blow things up.

I saw this video on facebook a little while ago and like a lot about it: it's a small project with cheap, easy-to-source materials, the girls can build a thing, and it's got fire and a fun flying payoff with a relatively safe and controlled amount of combustion. But I don't like that it's so fiddly.

Could you all please recommend your favorite explody crafts that:

1) Can be made in under an hour even by kids who aren't great with fine detail work.

2) Are INEXPENSIVE, do not require specialty parts, and can be sourced from a hardware store in an afternoon.

3) Are (relatively) safe to set off in a parking lot with a 10' distance radius.

4) Fly or go boom or have some kind of surprising payoff.

p.s. We've made rockets with alka-seltzer tablets before, which is fun, but we're ready for fire now. Thanks!!!
posted by phunniemee to Grab Bag (26 answers total) 15 users marked this as a favorite
I've had a lot of fun with dry ice, water, and 1-2 liter bottles. Very big booms. Assessments of danger and your own risk tolerance may vary. I plan to do this with my kid but not sure if I'd do it in a formal supervisory role. But if your group is down, it can be tons of fun.

Wikihow has instructions here, Wikipedia has info here.

If you live in an area with legal fireworks, I'd go that route. You can use them to blow up melons or paper effigies or lego buildings or whatever. They have their own dangers but I generally think that professionally made products are safer and more predictable explosives that something cobbled together based off internet recipes and assembled by children...
posted by SaltySalticid at 8:56 AM on May 16, 2017 [2 favorites]

Mentos and diet coke is a new classic. :)

as for fireworks - check with your council to ensure that you have clearance for a high-risk activity like that.
posted by heathrowga at 9:04 AM on May 16, 2017

Response by poster: Fireworks/firecrackers are not legal here and anyway they scare me and I enjoy all my fingers. No fireworks :)
posted by phunniemee at 9:07 AM on May 16, 2017 [2 favorites]

I don't know if this is too fiddly for your group, but popsicle stick chains (sometimes called "stick bombs") are cheap and awesome. There's no fire involved, but lots of popping and flying popsicle sticks.
posted by ourobouros at 9:33 AM on May 16, 2017 [3 favorites]

Here's a conflagration demo that's sort of similar to rocket candy, but geared towards kids.

Here's a kid-friendly version of the "elephant's toothpaste" demo.

You can take the basic "volcano" gas expansion and sort of "blow up" an apple.
posted by SaltySalticid at 9:36 AM on May 16, 2017

No fire, but bike pump + 2 liter bottle = water rockets (I remember doing this at camp as a kid and having so much fun I made my own rig to do it at home.)
posted by Wulfhere at 9:43 AM on May 16, 2017 [1 favorite]

A tissue paper hot air balloon has both fire (on the ground) and flying.

This site indicates you can use a heat gun instead of fire also.
posted by Wulfhere at 9:56 AM on May 16, 2017

Model rockets are really fun, and there might even be a badge for rocketry. A hobby shop will have re-usable rockets and the explosive 'engines' to power them. Ask around and post on freecycle.org; lots of people have rocketry supplies in the basement or attic. Parking lot is okay-ish, we went to the park.
posted by theora55 at 9:59 AM on May 16, 2017 [4 favorites]

The classic Potato Cannon was originally powered by hairspray (or more specifically the fire from igniting residue after spraying hairspray into a closed compartment). It only fits half your criteria, though - it's cheap components and would take about an hour but would be a group build rather than individual. And it would need an unreasonable distance to fire over. But apparently it comes in smaller sizes (scroll down)? Whether you want to arm your girls with potato pellet guns is a social question that only you can answer...
posted by aimedwander at 10:27 AM on May 16, 2017 [2 favorites]

Welcome to my favorite world! Baking soda and vinegar soda bottle rocket. The kid across the street wanting to make hollow pennies turned into hydrogen balloon explosions, which turned into a 4H group realizing that you could do the same thing with aluminum foil and muriatic acid too: Boom.

Related to Wulfhere's water rockets: If you take a 2 liter soda bottle, drill a 1/4" hole in the cap, cut a bike inner tube valve to just fit inside the cap, you can pump up the soda bottle, which gives more control than the dry ice bomb. If you pump the bottle up to 120PSI, put a nail through a stick and tap the bottle, it goes "boom* loud enough to wake the neighbors. Water helps muffle the bang. It's a bit harder to get a controlled explosion in a trash can, but this trash can is lined with a plastic bag because our first explosion blew holes in the side of the can: boom.
posted by straw at 11:04 AM on May 16, 2017 [2 favorites]

Oh, and just to elaborate on the hydrogen:

Do this with latex or nitrile gloves and with eye protection. In fact, do everything with eye protection. At some point I ordered a pack of like 20 or 40 kid sized glasses style eye protection. I give one to every kid who I do something with. "You mean, like for me, to keep?". Eye protection with everything is a good habit to get into, and cheap if you buy a big stash of them at a time.

Take a relatively narrow necked bottle (I used actual flasks from my chemistry gear). Pour in some muriatic acid (aka hydrochloric acid). Anyone with a pool, or who cleans concrete, will be able to spare you a beaker full, though you can buy it in two gallon packs at any home improvement store in the outdoor section.

Crumple up some aluminum foil. How tightly you crumple it controls the reaction rate, experiment. Drop it into the bottle. Take a balloon and put it over the mouth of the bottle, tie it on, wait a little while. When the balloon has expanded, untie it and remove it, tie it to the end of a long stick. Wave it over an open flame. I've found a propane torch is a good reliable ignition source.

And on the soda bottle rocket: You could also do this ala the bike pump method that Wulfhere's link suggests, but we put a thin piece of plywood with a slot in it around the neck of the bottle, that slid underneath the other thicker piece of plywood you can see in that video. Tie a string to that thin piece to pull it out quickly. This lets you build up more pressure than just forcing the bottle down around that cork.
posted by straw at 11:21 AM on May 16, 2017 [1 favorite]

I was also going to suggest model rockets, with the caveat that you should absolutely use the smallest motor size for the rocket or else you're never going to find them again once launched (ask me how many rockets I lost as a kid). "Easy to assemble" kits will take a lot of the fiddly assembly out of the equation; they're about $10 a pop. Launch system is about $30, and then motors are around $10/4-pack.

My misspent youth involved building a potato cannon and I would really recommend against it. I'm honestly surprised I didn't blow off a hand or the side of my face with the thing - Schedule 100 PVC is the classic building material but it really doesn't have the strength necessary to contain some of the forces involved. Curing PVC glue will also take well over an hour, and you really don't want to be firing it until it's definitively cured. You can punch holes in 2x4s with a decent spud gun (and put dents in siding, break small trees in half, the list goes on). They also may be illegal where you live, especially nowadays.

I did put a potato through the uprights on a football field, firing from the opposite end zone, which was pretty impressive at the time.
posted by backseatpilot at 11:22 AM on May 16, 2017 [5 favorites]

Aha, found it: Here's what happens when you blow up a soda bottle to 150PSI and then drop a screwdriver on it. I do not recommend this. There's a heck of a lot of energy in that bottle, which is why subsequent attempts were limited to 120PSI and we exploded them under water.
posted by straw at 11:29 AM on May 16, 2017

Model rockets are really fun, but be careful that you choose a legal launch site. Also please don't shoot off model rockets in a parking lot with a 10 foot radius.

If you want to do model rockets with your girls, I'd recommend you schedule something with NIRA (Northern Illinois Rocketry Association). You'll have to schlep everybody out to the East Branch Forest Preserve in Glendale Heights, but you'll be rewarded with a fabulous launching experience. Personally I recommend bringing your group to attend one of their public launches (usually the third Sunday of the month). There's one this weekend! We'll be there! Here is contact info for their Scout Liasion. The public launches are great fun. Even if you can't do it this time, it's worth looking into for future.

With regards to dry ice bombs: I wouldn't let someone else's kids make their own under my supervision. But I think they are fine for an adult to do in front of kids, with the following caveats: use 2 liter bottles, not 20 oz bottles, and use cold-to-room temp water, NOT HOT. Otherwise you risk a surprisingly sturdy bottle exploding with surprising force in your fist before you can throw it. When this happened to me, it took me a full minute to realize that I had not actually blown my hand *off*, and though I wasn't permanently injured, it took a few weeks for everything to work normally again. (It's also prudent to have a shovel or hockey stick or something that you can whack any duds with before you try to defuse them. Don't leave un-defused ones laying around.)
posted by telepanda at 11:31 AM on May 16, 2017 [2 favorites]

(Oh god, I'm old, I just realized film canisters are specialty parts these days, never mind.)
posted by The corpse in the library at 12:02 PM on May 16, 2017 [7 favorites]

You can make some hydrogen balloons and hydrogen+oxygen (2:1) balloons-- you can build a rig so that a kid can ignite one using a flame at the end of a stick that's 4-6 feet long, and use regular party balloons.

You can obtain tanks of both gases from your local liquid or compressed gas supplier, which may be a welding supply company.

Hydrogen makes a nice deep boom and offers a very short-lived fireball, and should be done outside in the dark, or can be done inside with very high ceilings (like a gym). The 2H + O balloon does about the same, but boom is even better since the combustion components are mixed. Here's a demo from the Royal Institution. You'll probably be using smaller balloons than this person.

You'll also get to see why hydrogen will never take over the party-balloon role when we run out of helium, despite also being lighter-than-air.
posted by Sunburnt at 12:23 PM on May 16, 2017

Burning steel wool looks really cool! you can start it off just by touching it with a 9 volt battery, and you can also sculpt the steel wool into a shape first and then film that shape burning away! this is how a lot of old visual effects were done, which is also cool.
posted by 5_13_23_42_69_666 at 1:02 PM on May 16, 2017 [3 favorites]

I'm here to second baking soda and vinegar. The ingredients are completely safe, and I had a lot of fun with it as a kid. Pour the vinegar into a bottle, jam the baking powder into the neck or lid (perhaps with some paper towel to hold it in place), close the lid, shake, and stand back. You don't need much; start your experiments with a small amount of each. If you can get your hands on corks or similar bottle-stoppers, so much the safer, since the bottle itself is less likely to explode.

(I also had fun at various times with blackpowder, propane, and the stripped ends of 120V extension cords, but I wouldn't recommend any of them from a safety point of view.)
posted by clawsoon at 1:49 PM on May 16, 2017

Check out some of the lecture/demonstrations from The Royal Institution, like this one: Fireworks and Waterworks - with Andrew Szydlo. Especially this scatterbrained old dude is obsessed withe FIRE and EXPLOSIONS and does a lot of cool things that aren't that dangerous depending...

We use to do the paint-can thing with calcium carbide + water (makes acetylene gas) or a quick spray of engine starter fluid (ether). If you can find or make a tube that will just fit a tennis ball you can make a mortar: put a hole near the bottom, put a nail through the tube a few inches up from the bottom, add boom fluid and shake, drop tennis ball down and light it up. (Back in the day, tennis balls came in metal cans so you could just cut the bottom off of one and tape two cans together to make the mortar.) We'd also dip the tennis ball in gasoline for a flying fireball but that's probably a little bit dangerous...
posted by zengargoyle at 2:08 PM on May 16, 2017

You may be interested in Backyard Ballistics for future adventures-- very useful as a kid between our actual backyard and scouting of all kinds. I was going to recommend Piezo Poppers too but see above on the film canister front-- maybe worth asking around though?
posted by jetlagaddict at 9:11 PM on May 16, 2017 [1 favorite]

Whatever you do, be careful.
posted by postel's law at 5:21 AM on May 17, 2017

This isn't exactly "blowing things up," but it's fire and impressive and quick so that many girls can have a turn (with proper supervision of course).

How to make grapes catch on fire in the micro wave (YouTube)

I did this with my daughter when she was young and it was great fun, if slightly irresponsible for a parent to show a young child.
posted by cross_impact at 10:32 AM on May 17, 2017

I've had a lot of fun with dry ice, water, and 1-2 liter bottles.

Please don't do this. My husband has driven friends to the hospital for emergency medical treatment after this very activity. Sorry to be negative, I am 1000% on board with Girl Scouts blowing things up, but safety first!
posted by beandip at 4:05 PM on May 17, 2017

Response by poster: Late update! We ended up making paper lanterns per a few youtubes I watched. The kind that are supposed to float. The girls had a blast constructing them and seeing how flammable vaseline is. Unfortunately it has rained literally every Girl Scout meeting we've had for the last few months, just terrible luck, and it was damp the day we made them and nothing worked. So I sent them home with extra supplies and instructions to the parents for a do-over on a clear evening. Thanks for all your suggestions!
posted by phunniemee at 7:11 AM on June 19, 2017 [2 favorites]

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