Center of Mass Fork Experiment

Center of mass (COM) it’s easy balancing act or a trick to try at home! All you need is 2 forks, a quarter, a cup, and some patience.

putting fork trick together (1)

Why does this look so weird? It all has to do with center of mass. COM is hard to define, but almost everyone has a great intuition for it! You find the COM of objects when you’re balancing things. Once an object is balanced, wherever you are holding up that object is where it’s COM is. You could probably guess where the center of mass is for a lot of symmetric objects. For example, a ruler’s COM is in the middle. But if you add some extra weight to the end, it’s COM will shift! 

rulers center changing (1)

A fork is pretty asymmetic, and that shows in it’s COM. 

Center of Mass Experiment

If you try to balance 2 forks on your fingers, you probably won’t win. This is where things get weird– the center of mass does not necessarily need to be within the object! For 2 forks, it ends up being just right outside of it. 

2 forks cm full (1)

Which makes the “trick” work. If you stick something, like a quarter, between the 2, now the center of mass of this collection of objects is now on the quarter. You will intuitively find the exact place on the quarter where the center of mass lies, when you achieve balance on something like the edge of a cup (pro tip: the more rigid the edge of the glass is, the better. We used the bottom of the cup here because that was less rounded, and hence stuck better, than the top of the cup). There you have it! Rather than thinking of it as a trick, think of it as you showing a weird property of physics in a simple way!

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