How Does That Work?: The Drinking Bird

Have you ever seen these little toys around?  You dip their beak in a cup of water, then the bird swings up and when he gets thirsty again, he'll dunk down and get some more to drink.  He'll do this over and over again. 

Can your students figure out why? 

The short answer has to do with evaporative cooling and vapor pressure.  For a longer answer, check here.

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How Does That Work is a series of products and demonstrations that you can present to your students and challenge them to explain the science of how they work. Make sure you decide ahead of time what you'll accept as a valid explanation - can it be printed straight off the internet, written in the student's own words, or does the student need to be able to explain it to you conversationally? What will a valid explanation earn the student - a prize, extra credit, a feeling of goodness?  

Friction: Give Yourself a Hand

No surface is perfection smooth – they all have bumps of ridges to a various extent.

Friction occurs when two surfaces rub against each other and those bumps and ridges catch on each other.

A notable by-product of friction is heat.

Have your students rub their hands together quickly. It doesn’t take much hand rubbing to notice a warm feeling.

Now put a small squirt of lotion (stick to unscented stuff for this) in each students hand.

Have them rub their hands together again – much less heat is generated.

The lotion acts a lubricant – it helps fill in some of the bumps and ridges on the surface of the hands, resulting in less friction and therefore less heat.

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Presented at the 2003 New Jersey Science Convention.

Bacteria: When Do You Make Me Sick?

Has this ever happened to you....

You wake up and head to school feeling fine.  By lunch you're starting to feel icky and by the end of school you're sick. 

Under the right circumstances, bacteria can reproduce every 20 minutes. 

Have your students determine how many bacteria will exist after 10 hours, if they begin with just one.  They'll have to do their calculations in their head/on paper, as a calculator will quickly become useless!

Scientists believe that humans can start to feel the effect of harmful bacteria when there are about 2000 bacteria in the body.  How many minutes/hours did it take to reach this number? 



If time permits and you're willing, you could use popcorn kernals to model the number of bacteria (up to a certain point....).  Have your students count out lots of 10 kernals in small cups - it makes it easier to count out 100, etc.

Volcanoes: Make a Model

You can find all sorts of volcano making/exploding kits to buy.  (If you're interested in buying, each of those words is a link to a different product).

But you can save your money and have a little more (messy) fun by making your own.

Start with an empty bottle - a Snapple bottle or soda bottle works well.  Tape it to a paper plate - makes it sturdier and easier to work with.

Mix up some paper mache.  There are all kinds of recipes out there.  I'm partial to just flour and water - cheap, easy to procure, and easy to clean up.

Dip strips of torn up newspaper in the paper mache and start applying them to the bottle.  Build up the shape of the volcano as you wish.  Make sure you keep the top of the bottle open!

By making your own model, you have the chance to make it the shape you want... make it a shield volcano, a cinder cone volcano, a composite volcano.  Even if you don't have a sepcific plan, it gives you a chance to review and discuss those types of volcanoes and how they're formed.

A cinder cone volcano

Allow your volcano to dry - the amount of time this takes depends on the weather and how heavy-handed you were with the paper mache.

Once the volcano is dry, you can choose to paint it. 

Or you can just get on with the exploding part.

Put some baking soda in the bttle.  You can add some red food coloring, for effect, if you wish.  Pour in some vinegar and stand back and watch!

And, if you're too impatient to build the volcano and just want to get to the exploding part, you can just put some baking soda in an empty bottle, add some vinegar and watch.  It's a good demonstration of a chemical change, even if you aren't studying volcanoes!

Cartesian Diver

Cartesian divers  are used to demonstrate the effects of air pressure. 

I used an eye dropper filled part way with water for my diver.  I put colored water in the eye dropper - I think it makes it easier to see what's happening.

Fill a large, plastic bottle with water.  Place the diver in the bottle - the diver should float at this point, make any adjustments you need to to make sure that happens.

Put the cap on the bottle.

Squeeze the bottle and watch the diver dive! 

Why does it dive?

When you squeeze the bottle, you compress the air molecules that are trapped in the bottle, including those inside the eye dropper.  When that air is compressed, additional water enters the dropper (since there's room available).  The additional water (and decreased volume of air) changes the density of the dropper enough to cause the dropper to sink to the bottome of the bottle.

When you release the sides of the bottle, the air trapped in the dropper expands, pushing out the extra water and decreasing the density so the dropper rises. 

A Cartesian diver can be used to explain all kinds of things, like how submarines work, how fish swim bladders work, etc.
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You can also use ketchup (or other condiment) packs as Cartesian divers.  In that case, water doesn't enter the packet, it dives strictly because of the change in density due to the compression of air molecules.

Books: A Short History of Nearly Everything

I've drawn attention to A Short History of Nearly Everything, by Bill Bryson before (not on this blog, but elsewhere).  I LOVE this book.  I find it utterly fascinating and fun to read.  It is Bill Bryson's attempt to understand the oldest questions posed about our universe and ourselves. In his words, "The idea was to see if it isn't possible to understand and appreciate - marvel at, enjoy even - the wonder and accomplishments of science at a level that isn't too technical or demanding, but isn't entirely superficial either."

In my opinion, he succeeded!

If you read it, you'll be amazed by how much we know about the world around us, and stymied by the vast amount of information that remains unknown. 

I am particularly fond of the analogies Bryson uses - I find that they make the material accessible as well as just plain fascinating.  He covers some pretty heavy topics, but the way he writes makes them understandable (and interesting) to even middle school students. 

Here are a few examples.

First, on how small a proton is...

 A proton is an infinitesimal part of an atom, which is itself of course an insubstantial thing. Protons are so small that a little dib of ink like the dot on this i can hold something in the region of 500,000,000,000 of them, rather more than the number of seconds contained in half a million years.

And then, on how large space is....

Our nearest neighbor in the cosmos, Proxima Centauri, which is part of the three-star cluster known as Alpha Centauri, is 4.3 light-years away, a sissy skip in galactic terms, but that is still a hundred million times farther than a trip to the Moon. To reach it by spaceship would take at least twenty-five thousand years, and even if you made the trip you still wouldn't be anywhere except at a lonely clutch of stars in the middle of a vast nowhere.

And, finally, on how little we even know about our own home....

The distance from the surface of the Earth to the center is 3,959 miles, which isn't so very far.  It has been calculated that if you sunk a well to the center and dropped a brick into it, it would take only fourty-five minutes for it to hit the bottom (though at that point it would be weightless since all the Earth's gravity would be above and around it rather than beneath it).  Our own attempts to penetrate toward the middle have been modest indeed.  One or two South African gold mines reach to a depth of two miles, but most mines on Earth go no more than about a quarter of a mile beneath the surface.  If the planet were an apple, we wouldn't yet have broken through the skin.  Indeed, we haven't even come close.

One of the other great things about this book is that you can pick it up, flip it open to a random page (or chapter) and start reading, as I did several times in looking for the above quotes. 

Get yourself a copy of A Short History of Nearly Everything - you can most likely get it at or through your local library.  Although, you might want to get your own copy so you can mark it up with your own notes, exclamation points, and underlining (although I gave up on all that when I found that I had underlined or bracketed almost every paragraph in the first two chapters).

Chemical Changes: Clean Your Silver

Line a non-metal container with aluminum foil.

Place tarnished silver in – make sure it touches the aluminum foil.

Boil water and add baking soda (1T per cup of water).

Pour this solution over the silver.

You'll quickly discover some shiny silver and may see a yellow haze on the aluminum foil.

I didn't fully submerge the lid, so you can see some of the tarnish at the top, and the "polished" part at the bottom.  It's not the best photograph, but it is nice and shiny (so much so that it reflects all kinds of other stuff and ruins my picture). 

Why:

The tarnish is silver sulfide, which forms from a reaction with sulfur in the air.   Sulfur has a greater affinity for aluminum than it does for silver.  So when you place the tarnished silver in the baking soda solution, the solution carries the sulfur to the aluminum.  The yellow haze on the foil is the sulfur that has been deposited there. 

The chemical equation:
Silver sulfide + Aluminum --> Silver + Aluminum Sulfide

Some Side Notes:
After hearing about this demonstration numerous times, I decided to give it a try (and get some pictures so I could share it with you).  It worked so well!  The yellow that's left on the foil isn't real apparent, although you could see an outline from where things had been sitting.  But, what was very apparent was the smell of sulfur, as soon as the solution was poured over the silver.  Wow!  I wasn't expecting that, but it certainly confirmed that the tarnish was composed of sulfur!  I'm now in search of a large enough vat to use to "polish" the teapot that goes with this lid! 

One more thing.... when researching the exact chemical equation I learned something else.... traditional silver polishes actually remove small amounts of silver along with the tarnish.  This method only removes the tarnish.  Seems like the way to go - no polishing and keeps the silver fully in tact!
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Presented at the 2003 New Jersey Science Convention.