I once had a science teacher who, anytime anyone dropped anything on the floor of his classroom, would say, “Gravity still works.” That kind of gravity is fairly easy for students to grasp, but what about center of gravity? Everyone and everything has one, but, because the center of gravity’s “location” can vary so greatly, it can be hard for smelly little kids like those that fill up your classroom on the reg to wrap their squishy minds around. To make the concept a bit easier to understand, we present this fast-and-easy Demo Science science demo.
Like A Tightrope But Completely Not At All, Really
All you need for this experiment is a yardstick and two functional arms, complete with hands and fingers. You were (most likely) born with the arms, and I’m pretty sure that every grade school classroom in America has at least a half-dozen yardsticks in it from the day it’s built, so you should be good to go.
Hold your arms out in front of you, just a shade less than a yard apart. Stick out your index fingers and have a student volunteer place the yardstick atop them. Slowly—SLOWLY!—start moving one of your fingers toward the center of the yardstick, keeping the other in its staring position, whence it shan’t move. The idea here is that you’re trying to make the yardstick lose balance and fall off your fingers. Ergo, slow and low is the tempo.
As you move your one finger (which we’ll call Finger #1) along, slowly—SLOWLY!—under the yardstick, you’ll notice that the yardstick is sliding over the top of your motionless Finger #2. Eventually, your fingers will be right next to each other, with the yardstick balancing atop both. Have a student or three try it for themselves (don’t pick Kevin), then ask the class as a whole what they think is behind this bit of naturally-occurring scientific magic.
When Finger #1 starts moving toward the center, the yardstick tips to that side as gravity (still works!) pulls the unsupported end down. As the yardstick tips*, its weight shifts slowly—SLOWLY!—off of Finger #2. Once that weight has shifted enough toward the center of its gravity, the yardstick will begin to slide over the top of Finger #2 as Finger #1 continues to move. Less weight equals less friction, which allows the yardstick to move. Conversely, the more the yardstick tips, the more weight and friction it puts on Finger #1; thus, Finger #1 will move toward center more “slowly”, allowing the balance to, um, balance out as your fingers slowly—SLOWLY!—come together.
* As The Yardstick Tips is the third greatest fake-soap opera name you will ever hear in your whole lil’ ol’ life. Write it down for posterity!