Thursday, April 21, 2011

How Many Drops of Water Can Fit on a Penny?

Materials
  • penny
  • dropper
  • water in a container (small plastic/paper cup)
  • plate/paper towel (optional)






    Directions
    • Have students observe a penny with a hand lens.
    • Have students predict the number of drops of water that can fit on a penny.
    • Use an eye dropper to place drops of water one at a time on the penny until the water runs over the edge of the penny.
    • Record the data.
    • Older children can repeat the experiment a few more times and calculate the average.


    If it is their first time doing this experiment, children will probably be amazed at how many drops can fit on a penny. Most students will underestimate the number.  Water molecules are attracted to other water molecules (cohesion). Molecules near the surface of a liquid pull toward each other. The cohesion of water molecules forms a kind of "skin" on the surface.  A drop keeps its shape because of this surface tension.

    Older students can brainstorm ways to change this experiment. Perhaps use a nickel or quarter. Try the back of the penny. What other ideas can students come up with?

    Another variation of this experiment is to use a cup of water filled to the brim. Have the students predict how many drops of water can fit in the cup without the water spilling over.  Have them use a dropper to add drops of water to the cup. They should count the drops and record their data.


    _________________________________________________________________________


    Let's try another experiment with  cohesion and surface tension.


    Materials
    • water
    • pennies
    • cup
    • plate/pan/paper towel to catch any overflow




      Directions
      • Place the cup on a desk or table with a pan/plate underneath to catch any overflowing water.
      • Fill the cup with water to the rim.
      • Predict how many pennies you can add to the full cup.
      • Slowly and carefully drop a penny into the cup.
      • Continue adding pennies in the same manner until the water spills/overflows.
      • Record the data.





        The water level actually rises above the top of the cup due to surface tension. The surface tension forms a kind of "skin" on the top of the water to hold the water together. Water drops are more elastic than we think!

        Linking up to Sunday Science

        10 comments:

        1. Thanks for the great ideas. They are always easy to exucute and I always have the supplies right on hand! And I do love the explanation about how they work out the way they do!

          ReplyDelete
        2. Wow, your blog is the first new, genuinely interesting one I have seen in a long while!

          Refreshing!! Well done.

          I am following you now and will make a point of coming back!

          Please feel free to drop over to our kid friendly blog.
          Maybe we could arrange a guest post in the future?

          Thanks again!

          http://beourbest.blogspot.com/

          ReplyDelete
        3. Such a cute experiment!! I will be trying it with my son :)

          Love your corner of the internet!!

          Came back to return the love and am now following your blog :)

          xo

          ReplyDelete
        4. I'm a new follower from the hop! I'd love a follow-back! Have a super weekend!!

          ~Holly
          http://www.twinsplusone.com

          P.S. I teach 2nd grade. :)

          ReplyDelete
        5. Cool looking experiment. Following from Wed hop!

          ReplyDelete
        6. i am going to try this with the kids! thank you.
          http://www.tanyetta.com/2011/04/follow-me-friday.html

          ReplyDelete
        7. I LOVE these experiments! You always have such great ideas and directions! Thanks for all you share! Deb @ LivingMontessoriNow.com

          ReplyDelete
        8. We haven't tried that one - it looks like it could be fun!

          ReplyDelete
        9. I haven't seen it with adding pennies to cups. What a great idea.

          ReplyDelete
        10. I did these experiments during President's week in my preschool class. http://www.brennaphillips.com/how-many-pennies-fit-in-a-cup-of-water-before-spilling-water-out
          http://www.brennaphillips.com/how-many-drops-of-water-fit-on-a-penny

          ReplyDelete

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