Amazing balancing fork trick
Surprise your friends at the dinner table!
Warning! Only under adult supervision.
- two forks;
- two toothpicks;
Intertwine the tines of two forks and insert a toothpick between them. Insert a second toothpick into a cork and set the construction on the toothpick, establishing a fulcrum for balance. Surprisingly, this balance will be stable! You can even make the forks rotate around the support.
A body is in equilibrium if all the forces that tend to move or rotate it (e.g. gravity and support reaction force) are compensated. When talking about the balance of our construction, we must consider not only the value of the forces acting on it, but also their points of application. Gravity acts on each part of the construction, but we can consider that it applies to the object’s center of mass. The position of the center of mass of a composite body depends on the relative location and masses of its parts, and may even be located outside of the body, as in our construction. If the construction is to stay balanced as it rests on the support, its center of mass must be on the same vertical line as the fulcrum. But that’s not all! It’s not enough to obtain balance: it must be stable! For the construction to be stable, it must be able to return from small deviations from the position of equilibrium, for example, when we gently strike one of the forks. For a body resting on one point, this means that the center of mass must lie below the fulcrum as well as on the same vertical line with it. The complex shape of our construction fulfills both of these conditions.
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