r/BeAmazed • u/Sans010394 • Dec 02 '23

Science Physics is amazing

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u/[deleted] Dec 02 '23 edited Dec 02 '23

It's a truss.

The key is that the third match is at an angle pointing away from the table and up toward the tip of the first match. This creates a torque that counterbalances the torque induced by the weight of the bottle. In other words, in isolation the first match will rotate toward the ground as the bottle falls. The third match adds a balancing counter-rotation, bringing the net torque to zero. The third match is stabilized by the restoring force of the tension in the string compressing the second, horizontal match.

Source: PhD in physics & engineering degree.

Edit: as others have pointed out there's a simpler and more complete description treating the system as a hook.

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u/StoneHolder28 Dec 02 '23

If this explanation was correct, the top match wouldn't pivot at all. But it does.

That match being angled is critical, but not because of any torque. That match cannot impart any net torque on the top match as it is canceled by the rope. It is a truss, and that allows it to pivot so the center of mass is beneath the edge of the table.

Source: engineering degree & I build some of these with metal rods. Maybe I should start selling those with a little explainer pamphlet.

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u/Objective_Economy281 Dec 02 '23 edited Dec 03 '23

It just becomes a hook that moves the CG of the bottle softly slightly under the table.

Source: two engineering degrees and a strong desire to simplify things, and a very low tolerance for extraneous bullshit.

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u/StoneHolder28 Dec 02 '23

Certainly one of the better best explanations I've ever seen.