Surface Tension Activities with Freebie

One of my favorite lessons to teach is on cohesion and surface tension.  The kids are naturally curious and very excited about it, so that makes my job pretty easy!  Here are a few fun activities we did today in class.

Soap Powered Boat Race 
 Fill a large pan with plain water.  Cut small boats out of card weight paper.  Provide students with cups filled with soapy water eye-droppers.  Students race to use the soapy water to break the water's surface tension behind the boat, which propels it forward.  When I demonstrated this for the class, I showed them how using an eye-dropper with regular water will not move the boat.  (The boat at the top of the photo loses the race for this reason.)

Cotton Race

Soap and heat reduce the surface tension of water.  This demonstration is great springboard for a discussion about why we use soap for cleaning our clothes!  This can be done with soapy water or with very warm water.  Drop a cotton ball into water and soapy water at the same time.  The cotton falls faster in the soapy water because it has less surface tension.  The lower the surface tension, the faster the water can move into tiny spaces (like the spaces between the cotton fibers).

Exploding Rainbow 

This one is probably the biggest hit with my 6th graders because it does a great job showing molecules in motion!  Fill a petri dish or glass pie pan with Vitamin D (whole) milk.  Place single drops of food coloring on the surface.

Add one drop of full strength liquid dish soap to the center and observe!  The soap breaks apart the cohesive bonds between the milk molecules (made of mostly fat, water and vitamins) which disrupts the surface tension.  This sends the food coloring swirling about.    GROOVY!

Shake'n Up Surface Tension

Pour a small amount of water in a small dish.  Sprinkle pepper on the surface.  Add one drop of soapy water to the center of the dish.  When the soapy water breaks the cohesive surface tension, the pepper rapidly scatters to the sides of the dish.  So simple...yet still cool! (Sorry for the low quality images on this one, I sent them on my phone.)

Freebie!

If you are looking to do some of these with your class, download this free activity packet from my TpT store.  It gives you a little more information about some different ways to teach surface tension!  Happy Teaching...