About Carolyn L

Carolyn coordinates the Science on Stage outreach program at HMNS and will blog about science toys and experiments, logic puzzles, and whatever else seems interesting at the time.

Sharky-Locks and the Three Gummi Bears

Need another excuse to buy candy this October?  Like cheap entertainment? Of course you do! How about some do-it-yourself grow-animals? For a buck or two, you can have a hundred edible expanding critters of your very own.

You need a few gummi bears or other gummi snacks (I grant you they are of questionable nutritional value, but they have their uses) and water. That’s pretty much it — see what we mean about cheap? 

I started with three gummi bears and one much larger gummi shark which had a disturbing layer of opaque white gummi on the bottom. 

If you want to know how much your gummi critters grow, you might want to trace around them or measure them, or just set some of your gummy snacks aside for comparison later. I had an electronic balance handy, so I used it, but that’s definitely not necessary:


The growing:  You need a container that can hold your gummi animals with a little room for expansion, and enough water to keep them covered:

And now we wait.  You may notice some expansion an hour after you begin, but your animals will look significantly bigger after 12-24 hours in water.  A few things to note: If you plan to eat your critters once they expand, please refrigerate them during the soaking process (this may slow their expansion somewhat, but you will also slow the growth of not-so-delicious bacteria). Whether you are refrigerating or not, set your critters somewhere and leave them alone as much as possible; if they jostle around too much, they may just dissolve and leave you with an unimpressive pool of colored sugar-water.

After a 20-hour soak, one of the bears intimidates his dry brother:


The “after” measurements:

This bear grew about three times as large as it was originally, and the shark about twice as large (it might have expanded further if given more time but it fell apart after being handled.)

Here’s a brief explanationof growing gummi snacks.

Extensions to try:  Soak your critters in distilled water, salt water, soda or juice, or try soaking an expanded critter in salt water.  Do some brands of bears hold up better or expand more?

(In case you were curious: Yes, you can spell it either way: gummi or gummy.)

Can you conquer the Tower of Hanoi?

Puzzles are very good at making you think flexibly and enabling you to find patterns (skills great for science and pretty much everything else), but they’re also just fun. One classic logic puzzle is the Tower of Hanoi, invented by Edouard Lucas in 1883.  This puzzle has been one of my favorites since I first saw it about twenty years ago.  As with many problems, there are multiple ways to achieve the basic goal, but after exploring you may figure out the most elegant or efficient way to get there.

One seven-disk version of the Tower of Hanoi looks like this (many more can be seen here):

The goal is to get the stack from the left pin to the right pin, finishing with the stack in the same order (largest disk on the bottom, smallest on top, and all the other disks in order). 

The rules:

1) You may only move one disk at a time. This means you may only move the topmost disk in a stack.

2) You may move the disk to any of the three pins, HOWEVER:

3) You may never stack a larger disk on top of a smaller one.

It’s easy to get the idea with just a few disks:

Here is the starting position:

Then we move the small disk to the middle pin:

Which allows the big disk to go to the last pin:

Then the small disk stacks on top of the big one and the stack is complete:

Try making and moving a three disk stack (just remember you can’t stack the larger ones on the smaller ones!):      

You can also use a dime, nickel and quarter, or three other coins of differing sizes, and just mark ‘tower slots’ on an index card in place of the pins.

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Once you get the three disk stack moved successfully, see if you can do it in only seven moves (two disks took three moves).  Four disk towers can be moved in a minimum of 15 moves.  You can also try this online. This version lets you choose up to eight disks and will keep track of how many moves you make.

Here are some things to think about as you play:

Do you start to see patterns in the way you move the disks?

Is there a rule about where you should put the first disk when moving a stack of three, four, five, etc.? Does it matter if the number of disks is even or odd? Does the pattern continue no matter how many disks you have in the tower?

What is the minimum number of moves for five disks?  Does this fit into any kind of pattern with the previous ‘minimum move’ numbers?   The minimum number of moves for a seven-disk stack is 127; does this fit the pattern?

One apocryphal story tells of a tower of 64 golden disks, which when completely moved, signal the end of the world.  Assuming one move every second, this stack would take over 500 billion years to move.

Check out this site for more discussion of the Tower of Hanoi puzzle.

Testing for the Best

Summer is here and one of the new Xplorations classes this year is Test for the Best, a class about consumer product testing (think Consumer Reports for kids: more about chocolate and toys and less about vacuum cleaners). I had fun checking out their experiments the past two weeks. 

How long does your chewing gum keep its flavor?  Does that battery really keep going and going and going?  Campers smeared fabric (in this case, socks) with chocolate sauce, ketchup and more before testing out stain removers:

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They also tested battery life, plastered themselves in bandages to see which ones would stick the longest, sampled chocolate chip cookies and created an advertising campaign for imaginary products, complete with slogans and fine print warnings!  Here are a few pictures:

The bandage line-up:

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 Some results from testing waterproof bandages:

 ed-bandage-indiv-1.jpg

Ready for a blind(folded) taste test:

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Working on an ad (and simultaneously testing markers):

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The slogan:

 ed-gum-slogan.jpg

And another group’s ad:

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Complete with a warning label:

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After rating many other things (microwave popcorn, cereal, etc.), on Friday the campers tested several things of their own choosing; bouncy balls, frozen treats, and chocolate bars.

ed-bouncy-ball.jpg 

We’re always looking for more ideas, so what do you think we should test in July?

Elephants and Chemistry

One of my favorite chemical reactions is frequently called “Elephant’s Toothpaste.”  It creates a LOT of gas from very little liquid, which makes an impresive show, and the main ingredient, hydrogen peroxide, is already familiar to most people. 

Here is series of photos of the Elephant’s Toothpaste reaction (sometimes very fun and very messy go together):

 etp-big-1.jpg      etp-big-2.jpg      etp-big-3.jpg       etp-big-4.jpg

If you ask someone what they use hydrogen peroxide for, they’ll usually tell you it can clean minor cuts and scrapes or that it’s good for household cleaning. 

When you pour hydrogen peroxide on a cut, what do you notice?  The first thing you’ll notice is that it stings a bit, but you’ll also see bubbles at the site of the cut. The bubbles are evidence that there is a chemical reaction; you started with one substance and ended up with something completely different (there was no gas before you poured the peroxide on the cut, and there were gas bubbles after, so the gas is new).

The formula H2O is almost universally understood as another name for water; this chemical formula indicates  two hydrogen atoms stuck onto every oxygen atom. Hydrogen peroxide’s chemical formula is H2O2, so you can think about it as water with extra oxygen attached. When you pour it on your cut, the hydrogen peroxide decomposes into liquid water (H2O) and oxygen gas (O2). The bubbles you see are oxygen bubbles.

In case you were wondering, oxygen atoms don’t like to hang around alone, so they bond to each other and that’s why we get O2 instead of just O.  If you are a person who counts atoms and you noticed that our atoms didn’t quite add up, you’re right; the balanced equation for the reaction is usually written:

2H2O –>  2H2O + O2

The large 2′s mean two of that whole atom (two hydrogen peroxide molecules can react to create two water molecules and one oxygen molecule). If the equation looks strange to you, don’t worry; just know that the molecules do the right thing.

What isn’t included in this equation is that the blood in your cut initiates this reaction (it contains an enzyme called catalase).

Something to try: 

If you have a bottle of 3% hydrogen peroxide at home, I have a project for you (if you are a kid, do this with your parents).

You need 3% hydrogen peroxide, yeast, dish soap, and a cup or bowl.  Most people face bigger hazards in the kitchen every time they cook, but it is a good idea to wear safety glasses or goggles just in case something splashes or falls and breaks, and hydrogen peroxide in your eye would definitely sting.

Put some yeast (I used about a teaspoon of quick-rise yeast) in the bottom of your container:

etp-yeast.jpg

Add enough water to wet the yeast and swirl it around or stir it a little:

etp-yeast-and-water.jpg

Now add a little dish soap and swirl or mix again:

etp-soap.jpg

You may want to set the container or a plate to help contain the mess before you add the hydrogen peroxide (I added approximately 1/4 cup (60 mL):

etp-hydrogen-peroxide-1.jpg

etp-hydrogen-peroxide-2.jpg

Here the hydrogen peroxide is starting to react and the soap catches the oxygen gas and it starts to produce foam.

But it keeps going:

etp-hydrogen-peroxide-3.jpg

And going:

etp-hydrogen-peroxide-4.jpg

And going:

etp-hp-5.jpg

And going:

etp-hp-6.jpg

The yeast contains catalase (your blood does too), and that helps the reaction happen faster, but the big thing to notice is that a small volume of hydrogen peroxide reacted to create a big volume of oxygen gas (the soap just helped catch it so we could see it better).  Any time you start with a liquid and make a gas, if the gas can expand, it will, and usually a lot.

Oh, and even though the reaction is called Elephant’s Toothpaste, please don’t try to eat it. Yuck!