Christmas Science Experiment: Santa's "Bag"

Santa's Magical "Bag" is a Christmas science experiment that you can do any time of the year! This fun science project teaches kids about water surface tension.

My kids were delighted when I told them we were going to do a science experiment with "Santa's Magical Bag." And when they saw that we were using real coins...they were even more excited!

And actually, you can do the same experiment without the Christmas theme...we just love to tie activities into Christmas during November and December!

To do your own "Santa's Magic Bag" Christmas science experiment, you will need four simple supplies: a cup, water, a pile of pennies, and a piece of red fabric or paper! I surrounded our work area with paper towels, but you could use real towels or do the activity over a pan.

Here's the easy How To:

1- Fill the cup all the way to the top with water. Look at it from the side and make sure the water is level with the top of the cup. Then make sure nobody bumps it!

2- Wrap a piece of red fabric or paper around the cup so it becomes "Santa's Magic Bag."

3- Show your kiddos the pile of pennies and tell them that Santa wants to take coins to everyone, but he doesn't know how many will fit in his "bag." Ask your children to hypothesize how many pennies will fit in the "bag." Our kids predicted 1, 2, and 5.

4- Let your kiddos carefully drop the pennies in one at a time. Count them together! As soon as we had two pennies in the cup, everyone wanted to change their hypotheses!

5- See how many you can get! And be sure to look at it from the side so you can see the water rise up over the cup in a big bubble. We only got 48, but that was because we had preschool-sized hands dropping pennies in...they can bump the cup pretty easily!

Make it an experiment: What I've already described is an experiment, but you can let your kiddos design their own experiments based on what they've discovered! Our kids tested different kinds of coins, different kinds of liquids, different kinds of cups, and...objects besides coins! Let them test and discover what they want to!

What's going on here? There are two basic principles (surface tension and adhesion) that create this Christmas science experiment, and they are both created by the polar nature of water. Water (H2O) is essentially a charged molecule: the side with the hydrogen atoms is slightly positive and the side with the oxygen atom is slightly negative. The negative side of one water molecule is attracted to the positive side of another water molecule. This makes water "stick" to itself (adhesion) and form a "surface" at the top of the cup. That surface will stretch and make the "bubble" of water you see when you place a lot of pennies in the water.

They are the same principles that allows insects and even a lizard to run across the top of water!

Do you like Christmas science experiments? Then you will love my ebook, 25 Christmas Science Projects for Kids! It's full of festive learning fun for you and your kids!