To float or not to float


Yet another activity involving soap and the reduction of surface tension, but probably visually more interesting than the previous two. It is also a simple activity for your child to see that surface tension is something real.

Start off by asking them if a paper clip (choose the small variety and not the bigger clips) will float or sink in water. Just to get the answer you want, show/remind them how other metal objects like nails and nuts sink. Then tell them that surface tension of water is strong enough to hold the paper clip up.

As your child might have some difficulty in carefully placing the clip on the surface in order to float it, I would suggest the use of paper towel for this purpose. The steps are outlined below.
  1. Tear a small square of paper towel (like Bounty towels) just big enough to hold the paper clip.
  2. Place the clip and paper towel on water. The paper towel will get soaked and will sink in a few seconds but the paper clip will continue to float. 
  3. Add a drop of soap/detergent somewhere near the paper clip.
  4. It might take a second or two -- the clip will suddenly go down like a brick.
Explanation: The surface tension holds up the clip. The soap reduces the surface tension and the clip sinks.



using paper towelpaper and clip on water

paper towel sinksadding detergent or soap

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