Friday, October 1, 2010

Balancing Act

If you drop a paperclip into a cup of water, it will sink to the bottom, because paperclips are more dense than water.  But, if you're careful, you can take advantage of water's unique properties and make the paperclip "float" on the surface.  

Fill a cup with water - the fuller the cup, the easier to do this.

Use a fork to gently place a paperclip on the water's surface.  You want to place the whole paperclip on the water at one time.  You don't want one part of the paperclip poking through the water. 

This definitely takes some practice and can be a test of patience.  I have never been able to get more than one paperclip to rest on the surface of the water, but I've seen others do multiple paperclips at the same time. 

If you get frustrated watching someone else get their paperclips to stay on the surface while you can't, place a drop of soap in thier water while they're not looking...


Water molecules like ot stick to one another, creating a membrane-like surface across the top of the water.  If you place the paperclips just so, that strong surface tension will support the paperclips (they aren't actually floating - they are still more dense than water).  Soap breaks water's surface tension, so you won't get soapy water to support anything. 

1 comment:

  1. The trick is to rest the paper clip on the edge of the cup and slide it onto the surface. Our record is 17 small paper clips at once, kids loved this demo of surface tension!

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