To most people, Center of Mass seems like a concept only high school and college aged students could understand. But my oldest son (who’s just entering second grade) recently came up with an experiment that introduced him to the concept of center of mass. As with many households, the fidget spinner craze has lasted through the summer in our house. My son recently bought himself a light up fidget spinner, with replaceable colorful lights that blink after being pressed. Since the lights can be taken out, I made sure he knew to keep his new toy away from his little brother, who sticks everything in his mouth! But being able to remove these lights opened up an opportunity for me to teach my son about center of mass, and its affect on rotational movement.

It all started after he played with a friend’s light up fidget spinner. He begged for me to take him to the store to find one. After a couple failed attempts with me, he eventually found one during a quick trip to the store with dad. Once at home, he started playing with the fidget spinner, and noticed his new toy acted strange when he took the lights out of the spinner. He showed me, and asked me what was going on. I told him I’d explain it to him while he did a little experiment!

Center of Mass Experiment with a Fidget Spinner

To understand why my son’s fidget spinner was acting strange, we did the following experiment!

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Supplies:

-1 light up fidget spinner

Changing the Center of Mass of our Fidget Spinner

Step 1: We started our experiment by seeing how the spinner spun with all the weights in. His spinner spun just as it always, smooth.

Step 2: Next my son took one of the lights out, and watched how the spinner changed. He noticed two things:

1. The spinner “wobbled” as it spun.
2. The spinner no longer spun as it slowed down, but swung back and forth.

I told him the change was due to moving the center of mass (COM) of the spinner. When he took out one of the lights, the COM moved from the middle of the spinner to a new spot closer to the other two lights.

Step 3: My son removed a second light, and spun his fidget spinner.

By removing another light, he moved the center of mass closer to the remaining light. He noticed his fidget spinner continued to wobble when it spun, and swung back and forth as it slowed down.

Step 4: Last my son removed the remaining light from his fidget spinner.

He noticed his toy no longer wobbled or swung back and forth when it slowed down! I told him he had returned the center of mass to the middle of the spinner, so it acted just like if all the lights were back in place!

My son continued to play with his spinner, taking the lights in and out, and exploring how his fidget spinner changed. He noticed that with all 3 lights in or out of the spinner, the toy continued to spin around the center until it stopped. When he would have only 1 or 2 lights in the spinner, it would wobble, and swing back and forth when it slowed down.

Center of Mass can be a difficult concept to grasp when learning about it through a text book, but when it involves a fun toy, it is so much easier to understand!

Interested in other science activities? Check out some of my other posts!