Floating Paper Clips (Demonstration)
 

Surface Tension
 

Purpose:
Illustrate the idea of surface tension
 

Safety:
No precautions

 
Materials:
1.
Paper clips
Dish soap
Large clear container

2.
Penny
Eye dropper

 
Procedure:
(1.)  Fill large container with water.  Carefully float paper clips on top of the water.  Squirt one drop of dish soap into the container and watch the clips sink.
(2.)  Have students guess how many drops of water can be placed on the surface of a penny (about 50!).  Notice that thickness of the water layer is about 3 times that of the penny.
 

Explanation:
(1.)  The hydrogen bonding in the water (surface tension) is strong enough not to be overcome by the minimal weight of the paper clips, however when soap is added these bonds are broken down and the water can no longer retain its same bonding characteristics.
(2.)  Same thing, except when the water surface breaks, it is the force of gravity which outdoes the hydrogen bonding forces, the drop just gets too “heavy”.
 

Clean-up:
All solutions can go down the drain; save the clips and pennies
 
 
 

Ginger Chateauneuf, 2000.
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