By Tami G. O’Connor
When I taught second grade, one of our literature books was Mirette on the High Wire by Emily Arnold McCully. I was that teacher who always taught thematically—that is, nothing ever was taught in a vacuum. I tried as often as possible to tie things together.
So as we read this book about a young French girl who learns from a retired high-wire artist to walk on a tightrope, in Language Arts we talked and wrote about our heroes, in Geography we researched where in the world France is. And in Science, we learned about balance and center of gravity.
Even young children know that if you hold something above the ground and release it, the object falls. This is due to gravity. Gravity is the force that pulls all objects on Earth downward. Center of gravity is simply defined as the point where the mass (the stuff things are made from) of an object is concentrated.
This point of concentration is where an object balances. For example, if you take a Popsicle stick and tie a string around it, the stick will balance when the string is located at its center of gravity. For a simple object like a Popsicle stick, the center of gravity is located right in the middle of the stick. If you tie the string too far on one side or another, the stick will not balance.
But what happens if you add a pea-sized lump of clay to the same Popsicle stick that just balanced perfectly when the string was tied directly in the center? Like a seesaw, the stick tips in the direction of the added weight. In order to rebalance your stick, you will need to slide your string closer to the weight.
The result is that in order to balance, the stick will be longer on one side of the string than the other. In this case, the students can easily see that the center of gravity moves toward the added weight.
For more complex shapes, the center of gravity is not as easy to find. If you look at the human body, the center of gravity is actually found a little above the waist. This is because there is more mass above your waist than below it.
While teaching Mirette on the High Wire, I would demonstrate the Popsicle stick and string. Next, I asked the Physical Education teacher to pull out the low balance beam and have the kids explore walking on it with their arms at their sides versus holding their arms outstretched, with and without weights. The result was always greater interest by my students and therefore greater understanding of the concepts presented.
One of the activities I did with my students was a science/art project in which we made Balancing Men. You can make your own tightrope-walking men or ladies from Popsicle sticks, pipe cleaners and a pair of washers. Colored markers and googly eyes are optional, but add a lot of cute balancers! These balancing people were simple to make even for younger learners.
Student were able to experiment with how wide apart they needed to place the arms in order for their little men to balance. Once they mastered having their “walkers” balance upright, I challenged them to balance their Popsicle stick so it was horizontal. This led to plenty of discussion on center of gravity and why tightrope walkers use poles to balance themselves as they walk.
As an extension, we also made balancing birds.
manilla file folders
balancing bird template (click on image for printable PDF template)
2 coins (nickels or quarters)
crayons or colored pencils (optional)
If you would prefer not to have your students make these designs, or if you’d like a more durable example of center of gravity for your science table, Educational Innovations carries a number of engaging products that students find fascinating!
A fascinating conversation piece that illustrates the principle of center of gravity! A small hole in an oak board allows you to balance a 2-liter soda bottle at an angle that appears to defy gravity. Use as a teaching tool or a centerpiece at your next party!
This eagle balances on almost anything – your finger, a pencil, or the edge of your desk. Its center of mass (or center of gravity) is directly beneath the tip of its beak. Students can change the eagle’s center of gravity by adding small pieces of tape. Our proud bird can even be used to demonstrate rotational inertia! Just balance it on a pencil above your head, and turn around 360 degrees. The bird will remain in the same orientation due to its fairly large moment of inertia.
This is a ‘must have’ for your science table. When assembled, this mysterious device will balance upon a point or slide down fishing line from one side of your room to the other. Students can easily bend the wires so that it balances at different angles. It demonstrates the advantage of keeping a low center of gravity.