Science Week 8: Gravity

A couple of resources to start you out for gravity.  First of all, the Let’s Read and Find Out title was Gravity is a Mystery by Franklyn Branley was a bit of a disappointment.  Unlike most of the Let’s Read and Find Out books, I didn’t feel that this one did a very good job at explaining gravity.  I’m not a scientist, so I really invite someone who understands physics better than I do to correct me if I’m wrong, but don’t scientists think they understand gravity reasonably well?  Why one object should attract another is never anything I’ve seen explained fully, but the basic concept makes sense.  However, this book kept insisting that scientists don’t even really know what gravity is.  The fact that gravity causes an attraction, not just to the earth, but also between all objects, was never mentioned in this book.

I much preferred the simpler, but useful book I Fall Down by Vicki Cobb.  I wouldn’t have minded this sparse picture book having a little more information.  However, it did do something very nice by warning the reader that you’ll need a number of household objects around to illustrate the concepts in the book.  I hate when I’m reading a science book that seems like it’s a text and it suddenly tells you to get up and do an experiment out of the blue.  It’s nice in concept, but sometimes I don’t budget our time for it or have the materials ready (even if it’s just a dishcloth or a scale).

My favorite book of resources this week was The Science Book of Gravity.  I’ve really been enjoying this series, which is from the early 90’s.  The experiments are all pretty simple, but focus on fun.  Not everything we’ve done from this series has worked, but most of the experiments have.  This week, I took nearly all our experiments from there.  I didn’t find anything simple for us to use from the Janice VanCleave book about gravity.

We began with an experiment that you absolutely must try, even if physics isn’t your topic this year.  I rank this among the truly excellent home science demonstrations I’ve seen in my life.  Here’s what you do:

  1. Take a small water balloon and fill it with water.  It should be about the size of a clementine or maybe a tangerine.  A grapefruit is too big.
  2. Open the mouth of a regular balloon very wide and have a partner put the water balloon inside the regular one.  Roll up the mouth so that the water balloon is inside.  Both balloons have some give, so it may take some shimmying, but it can be done.
  3. Blow up the regular balloon and tie it.
  4. Now play with it.  The center of the balloon’s gravity isn’t where you expect and it constantly moves, causing the balloon to act in unexpected ways.  Trust me.  We all giggled as we tried to throw and catch it.

Nothing we did topped that, but we did do a few other fun things.  We built a marble run to think about how gravity pulls us downward all the time.  We weighed ourselves.  We made a simple scale and “weighed” objects by hanging them on a rubber band and seeing how much they pulled on the rubber band.  We also dropped a large combination of objects and watched to see if they hit the floor at the same time.  We dropped some of them into modeling clay (though I realize now Play-doh would have worked better) to see what type of object made the biggest dents.

We enjoyed a couple of good videos.  First, the Eureka video on gravity was a good one.  I’ve posted about this series before, so I’ll just link to it.  You can see it here.  We also, of course, enjoyed the Bill Nye episode about gravity.  Finally, did you know there’s a Schoolhouse Rock video about gravity?  Well, now you do!

Finally, we did one last fun experiment.  Using modeling clay (this was really a modeling clay heavy week), we stuck marbles into one corner of a jar lid.  If you place the lid on a slope with the marbles slightly to the upper end of the slope, the jar lid with roll upward.  But it’s not defying gravity!  The marbles are the heaviest things and they need to go down the quickest way.  Anyway, three of our four lids failed because they weren’t flat on the edge, so make sure you have a completely flat rimmed lid for this one.  Below is a picture of the inside of one of the lids that did not work.  Alas.  But you get the idea.

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