I like to call it "Wet Presidents." First, we made predictions as to how many drops of water would fit onto a penny, nickel, dime, and quarter and wrote them down in crayon (so we wouldn't try to change our answers). I have to say that the guesses were really low so I knew they would be into this to see how many actually would fit.
Then we began our experiment. One partner did the drops while the other kept track with the tally marks. (We of course switched for each coin!) Then when it spilled everywhere we stopped and counted the tally marks. AmAzInG!!! They couldn't believe their answers.
So we talked in "first grade talk" why so much water would fit and what were some good tips to follow to get the most water on the coin. We had some extra time left so they got to do it again with 2 new variations--try to beat the number of drops from the first time AND use a magnifying glass to check out the drops on the coins. Way cool!