Science Experiment: Finding the Center of Mass

We usually do a little science experiment every week (sometimes more, sometimes less). We were reading about center of mass (or center of gravity) today and the suggested experiment looked quick and easy, and we had all the materials. Those are the 3 key factors for us to do experiments. We save the more complicated ones for special occasions or homeschool co-op days. I thought a good way to chronicle our experiments would be to post about them.

This one was so simple, the big boys all poo-pooed it so Tiger Boy (7) and Dragon Boy (4)  were my assistants. Of course as we were really getting into it, the big boys noticed we were having fun and decided to kind of join in (i.e., watch from the sidelines and offer suggestions/criticism).

Our mission today was to find the center of mass for an unusually shaped, flat object. Technically we are finding the geographical center since this is a 2D object (not 3D). The geographical center of North America is supposed pretty close to us. I wonder if this is how they figured it out. We might have to trace a map of North America and try it out :-)

Step 1: Talk about center of mass (center of gravity). We use Answers in Genesis, God’s Design for the Physical World: Machines in Motion. If you don’t have that set, no worries. There are plenty of resources online to read/watch.  Just use our good friend Google.  Here is a little video we found (plus it has another little experiment that’s easy to do).

We also talked about why this is important and how it’s applied (examples were balancing acts with multiple people, riding a bike, doing handstands, touching your toes like in the video).

Step 2: Gather materials

  • cardboard or stock (nothing too flimsy, a side of a cereal box will do)
  • pencil
  • scissors
  • hole punch
  • string
  • nail

Step 3: Draw an unusual shape on your cardboard. Here is Tiger Boy’s creation. The first shape was a little small so I asked him to draw as big of a shape as he could fit on the page. And then we cut it out.

Experiment: Center of Mass

Step 3: Hypothesis! I asked Tiger Boy where he thought the center was and then we marked it boldly.

Experiment: Center of Mass

Step 4: Punch 2 holes not directly opposite from each other.  90 degree angle from your proposed center would be good. (Our experiment said to do 4 holes but 2 well placed holes are all that is really needed).

Experiment: Center of Mass

Step 5: Hang on the wall. We utilized a hole that was already in the wall. Take your sting and tie a loop on one end and something to weight it down on the other end. This is a great opportunity to explain what a plumb line is.


Step 6: Draw a line along the plumb line. Repeat for second hole. Where the lines meet will be the center of mass.  Tiger Boy was pretty stinkin’ close.

Experiment: Center of Mass


Step 7: Balance the blob where the lines intersect on your finger tip.

Experiment: Center of Mass


There you go. Super simple experiment.





1 comment to Science Experiment: Finding the Center of Mass

  • kami

    We have been to the geographical center of North America, it’s worth the fun day trip. If you have the book North Dakota day Trips you could probably stop at a few things on the way there and back. Also Belle Fouche South Dakota is the geographic center of the United States, so if you ever go down to Mount Rushmore you might want to take that route.

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