## Sinkin' Lincoln!

Looking forward to the President's Day holiday next month we have an experiment we always include in our celebration. We demonstrate the unexpectedly strong force of surface tension by "soaking" (with the utmost respect) our 16th President.

When done carefully, a lot of water can be made to sit on a coin without falling off.

OPENING DEMO....

Have available an almost-full flask or bottle containing colored water. Using a dropper (and with much drama) ask the children if the container is "nearly full." Very carefully (with even more drama) use the dropper to add more water, with the children watching to see when it begins to OVERFLOW! You will be amazed to see how many more drops it takes to reach overflowing.

EXPERIMENT DEMO for the students ....

Since it is President's Day (or thereabouts) my opening question asks, "Whose picture is on a penny....?"
Place a dry penny, with the head side up, on a table and, using a dropper, count how many drops of water will fit on the top of that penny (much suspense!) before overflowing.
Emphasize dropping SLOWLY - have children practice with the droppers before starting their own experiments.(My personal record of "drops on a cent" is shown below.)

EXPERIMENT

Now set up the children in pairs with penny, dropper, water, paper towel, pencil and paper. They will now do what scientists always do.......watch, measure and write results.
One child uses the dropper, the dry penny and the water while the other counts the drops to overflowing and records the results. Then they change places and repeat the procedure.

CONCLUSION

So OK, the resulting numbers of drops recorded may vary widely since kindergarteners and first graders do count erratically (I've watched counting series that jump from hundreds to thousands and back again) .... and they make numeric notations erratically (sequence ..... what's sequence??) but amongst everything going on they have noticed that the liquid state of matter has a "skin" shaped almost like frosting when it's carefully piled on a penny, hence .......... "Sinkin' Lincoln."

With second and third graders, the closer results set can be charted on the chalkboard with the variety of representations and statistical measurements ... mean, median, mode, lowest, highest (of course!) and experimental variations considered. Does the date on the coin matter? ... the size of the dropper?.... the type of liquid? ... the type of coin?

We have tried repeating the experiment with maple syrup, with predictably tasteful but messy and chaotic results.

We have also retried the experiment with the twenty-five cent coin since it has the image of the other president we celebrate on this holiday. Our drop counts this time were below predicted amounts because, in spite of the larger area of the quarter, President Lincoln's penny does have THE EDGE over President Washington's quarter. You can check this fact with a magnifying glass!
Also use the magnifier with a penny to see the statue of Mr. Lincoln inside his memorial building on the obverse of the penny - a wonderful discovery for many children.

(My personal SINKIN' record with water, an eye dropper and a 1991 penny is 46 DROPS.)

For some interesting penny facts check the following websites:

The PENNIES FOR HOPE School Project shows the initiative taken by one school to console and improve the world through pennies.

SMALL CHANGE - Thoughts on a Penny with many, many facts about this coin which is minted just a few blocks from here.

COIN SPECIFICATIONS from The U.S. Code spells out the precise rules in coinmaking.

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