Thursday, May 21, 2009

Science Saturday Challenge #9

Surface Tension

Water is an amazing molecule for many, many reasons, one of which is it's incredible surface tension. First read this article: Sticky Water from the Exporatorium to get an idea of why water has such adhesive abilities.

A great book about water, including surface tension, with stunning pictures is A Drop of Water by Walter Wick.

These experiments are easy to do and visually impressive, both of which make for favorite science experiments in our house!

A small bowl of water
Liquid soap (for hands or dishes)

Sprinkle pepper onto the surface of the water until it pretty much covers it.

Dip a clean finger into the bowl of water, and Ds#2 and Ds#3 are doing in the picture below.

Now rub your fingertip with a little of the liquid soap and dip it back into the center of the bowl.

Now try the experiment with milk and food coloring for a more dazzling display!

Soap has a polar "head" that attracts the hydrogen bonds of the water, but also has a hydrophobic "tail" that stick up at the water surface. When the water bonds to the soap the tails break up the surface tension. That makes the pepper and the food coloring scatter, and gets dirt off of surfaces!


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L a u r a said...

That is a fun experiment--and easy enough to run in the kitchen and do it right now! Thanks!

School for Us said...

Thanks for the comment about my ladybugs! I thought we were about done with them, and just discovered a bunch of pupa on one of my bushes! So, I guess I better keep my camera handy. :-)

I love this post! I especially love your boys' enthusiasm. :-) I think we'll have to check out that book and give these experiments a try.

Do you plan on continuing these challenges during the summer? Either way, I hope to either do your new or some old challenges this summer. You've got lots of great experiments! And you make learning so much fun!

Kris said...

I hope so. I'm doing another webinar on June 30th--in fact, I need to post about that!

We're always doing something spontaneous during the summer, usually science-related...