Science Experiments for Unimpressed Kids: Surface Tension

A while back, Eli and Liza excitedly talked about water striders. “They walk on water, dad!”

As a scientist, I never miss a teachable opportunity. “You know why water striders can walk on water?” I asked them. “It’s because of surface tension. I’ll show you!”

How to Demonstrate Surface Tension

This easy and fun experiment will be sure to captivate absolutely no one.

Equipment

  • Glass of water
  • Needle
  • A piece of toilet paper
  • One or more kids who will be unimpressed by your experiment
  1. Tear off an amount of toilet paper that’s small enough to fit in the glass but large enough for the needle to rest on it.
  2. After you make sure your fingers and the needle are dry, place the needle on the toilet paper.
  3. When the kids ask why you’ve taken toilet paper out of the bathroom, explain that you’re going to use it to make a needle float.
  4. Place the toilet paper and needle on top of the water.
  5. Tell the kids, “Watch! Watch what happens when the toilet paper sinks.”
  6. Wait for the toilet paper to sink.
  7. Keep waiting.
  8. When the unimpressed kids wander off, tell them, “Don’t go anywhere! It’s about to happen!”
  9. Poke at the toilet paper to try to make it sink.
  10. Poke some more, until the needle sinks and you realize that you’ve splashed water on the needle, ruining the experiment.
  11. Say to the kids, “No, it’ll work, I swear. Just let me try again.” Ignore them rolling their eyes.
  12. Dry off the needle. Repeat steps 1 through 4.
  13. This time, be more careful when you poke the toilet paper and make it sink.
  14. With the needle floating on the water, excitedly say, “Kids! Come look! The water’s surface tension is holding it up.”
  15. Start to explain that the liquid is made up of molecules that are like small magnets and pull towards each other, which lets them hold up the needle. Stop when you realize the kids aren’t listening.
  16. Instead say, “If you look carefully at the water you can see where the top of the water is being pushed down by how the lights reflect off of it.”
  17. When you move the glass to better catch the light, slosh the water so that the needle sinks.
  18. Give up and let the kids wander away.
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6 Comments

  1. katre
    on November 28, 2011 at 9:44 pm | Permalink

    This sounds suspiciously like our attempt to put celery in red food coloring and make it turn red. After an hour it was faintly reddish and Z asked, “Can I eat the celery now?”

  2. on November 28, 2011 at 9:52 pm | Permalink

    Ha ha sigh.

  3. Gary Mitchel
    on November 29, 2011 at 3:03 am | Permalink

    HA!

    Also, this could so be a DC*TV sketch. A take on Mr. Wizard, but where none of the experiments work…

  4. on November 30, 2011 at 2:30 am | Permalink

    So when are you breaking out non-Newtonian fluids? I think Liza would take the “keep running” instruction at this point.

  5. bibliovore
    on November 30, 2011 at 2:42 pm | Permalink

    Reminds me of the Newton’s Cradle scene in Rosencrantz And Guildenstern Are Dead.
    Here, at 6:35 –
    http://www.youtube.com/watch?v=ftd4AMPFk2I

  6. on November 30, 2011 at 5:11 pm | Permalink

    Geof: That’s a really good idea. I’ll have to try it.

    bibliovore: Ooh, good reference! I’d forgotten about that scene.