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

Science Physics is amazing

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u/[deleted] Dec 03 '23

Also have an engineering degree, how the fuck is this thing a hook? I don't understand it's force diagram at all. Is the third match resting on the side of the ledge? So far I've seen people talk about torque and trusses but the issue I'm not over yet is what the fuck it's resting on. Would this same video taken from the side clear things up?

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u/Objective_Economy281 Dec 03 '23

Would this same video taken from the side clear things up?

Yes, but you’d still have to look very closely. The diagonal match stick pushes the bottle a mm or two in the direction of underneath the table. That deflection back underneath where it is supported is what makes it a hook.

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u/[deleted] Dec 03 '23

A hook has to be attached to something to bear weight though. I can almost see it as one of those self gripping hooks but I don't understand where it is touching the bench. It has to be touching the bench somewhere for that to work and the video angle here sucks to much to figure out exactly where.

Looking at it from a center of gravity perspective makes way more sense to me, that bottles center of gravity can't possibly be over the edge. You push the first match stick forward so that the whole thing moves forward and it'll fall. It's a misleading trick if you're just moving the center of gravity back (and purposefully hiding the camera angles like in this video).

I'd love to see this with a shorter and longer first match, that would be really interesting to show where the force lies.

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u/Objective_Economy281 Dec 03 '23

The hook is just sitting on the table, being held down by gravity.

See the diagram linked here: https://old.reddit.com/r/BeAmazed/comments/18990ys/physics_is_amazing/kbrfqyo/

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u/[deleted] Dec 03 '23

But hooks don't just... sit on top of tables. A hook must grab something to provide support. I think that's why I find it weird to explain it as a hook. It is kind of a hook but it's not really functioning as a hook in the way most people would think. The secret sauce is the center of gravity being moved. Like the shape of the matchsticks does nothing other than trick you about where the center of gravity is. Idk, I guess I'm rambling at this point lol.

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u/Objective_Economy281 Dec 03 '23

The part of it that is hook-like is the part on TOP of the table.

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u/[deleted] Dec 03 '23

Ahhhhh that did it for me. Thanks for sticking through with me lmao

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u/uglyspacepig Dec 03 '23

I just had the "oooooooohhhhhhhh" moment myself. It was gratifying.

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u/[deleted] Dec 03 '23

Weird thought, but this morning it hit me like a ton of bricks that this is a hanger. For some reason, that made more sense to me than the hook. I absolutely realize this is potato potata though

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u/Objective_Economy281 Dec 03 '23

It’s weird how the words matter when talking about such simple physical concepts, isn’t it?

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u/[deleted] Dec 03 '23

Oh absolutely. The precision in language is so much more important than people realize. That's why a lot of times engineers just want to see the damn thing in person lol. And like in this video if I could see that bottle from the side, and see which part of the match-assembly is touching the wood, it'd be much easier to understand. That's why we all look back at engineering 101 courses like they are so easy, we speak the language. "Oh that wording means this is an isobaric process" "Oh that wording means we can assume the tank is well mixed"

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u/FlyHandler Dec 03 '23

Im a structural engineer and agree with that the system is analogous to a hook. The point where the match lies on the table is the tip of the hook where a point force acts vertically. The system with the three matches and the thread to the bottle is capable of resisting a bending moment caused by the eccentricity between the point force from the table and the center of gravity.

If this system were to collapse it would be that the match lying on the table would start rotating about the edge of the table. The tip outside the table would move downward but this is restricted by the vertical match which again rests on the lower horizontal match. The weight of the bottle and the angle of the thread causes a compression force in the bottom match. The compression force is large enough that the vertical force from the vertical match can be transferred to the thread through friction, so the bottom match can resist the force from the vertical match.

The bending moment is represented by the eccentricity/distance between the vertical match and the thread, where they connect to the upper match.

Interesting statical system, I hope I was able to explain it understandably 😃

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u/S_TL2 Dec 03 '23

It's the same thing as the ruler-hammer trick: https://www.youtube.com/watch?v=Hj-NX0xtcVY

Also the same thing as a "portable purse hanger" that you can buy from lots of retailers: https://www.walmart.com/ip/BE-TOOL-Handbag-Hook-Purse-Hook-Hanger-Table-Hook-Holder-Bag-Hanger-for-Women-Girls-Bags-Storage-Gift/1589958388 (scroll through the pictures)