Stupid Physics Trick #4 - The Bar Trick

[@dannydiaz5675]

I love how she explains it! Gonna try to do it tomorrow! Thanks for the video!

[@dannydiaz5675]

IT WORKS!!!! At first try I failed, but then it worked perfectly, and we were all amazed XD

[@heroichitsuji]

Me: Looking for an explanation The physicists: Well we’re physicists so we have to free body diagram it me: YES!

[@nizammahazir7027]

Still didnt understand

[@joeimaverage4424]

Cancel gravity, Awesome.

[@ChaseR28_]

The FBD has bothered me for a really long time now. The no torque from the tension is fine, but that should be the end of the story. The normal force shown can't exist because the matchstick isn't lying flat; it rotates ever so slightly, maybe only two or three degrees. But if it did lie flat, the diagonal matchstick's force still wouldn't make sense. It's implied the force comes from compression against the first match but the compression has an equal and opposite force into that first match as well. It can't push on anything.

[@bababoi9078]

This is because the bottles weight is distributed on two separate points. But not evenly

[@bababoi9078]

Okay ive been thinking about this question. Its bugging me alot.

[@realistic_holder1571]

The FBD is is wrong. what really happens is that the centre of mass of the bottle is pushed by the slanted match slightly backwards behind the edge of the table.

[@SR-bu6kz]

What about the component horizontal force from the diagonal matchstick?

[@baraskparas9559]

Magnificent demo.

[@mln-mal]

She is a very nice teacher

[@Naked_Snake]

At 3:20 you say the tension is at the pivot point, but really the string is ever so slightly in front of the table. How does it still not tip considering this fact? Is it because of friction?

[@Prof-Hafner]

Yes so really the string is applying a bit of clockwise torque (along with the table). So that just means the diagonal matchstick has to apply even more the other way (counterclockwise). It can do this because the static friction force between the top match and the table that it is pushing against can take a variable value, up to the maximum mu*N, if you know what I mean. If the coefficient of friction is too low, the diagonal matchstick will make the top one slide and it won't work.

[@Naked_Snake]

@@Prof-Hafner That makes sense, thanks!

[@DoppaD]

The trippiest part was the glitching from 2:30 to 2:33

[@Prof-Hafner]

One of us miss spoke and it was cause lots of confusion so I headed it out.

[@dandooni1326]

How will a measure of a turning force hold a mass?

[@Moncef3117]

That's because the net torque is 0 by the additional matches sticks

[@ankk98]

mind blown

[@arpitchaudhary5524]

Maam, what is role of centre of gravity in the above experiment video?

[@Prof-Hafner]

In general, when something hangs in a stable configuration, the center of mass must be directly below the pivot point that the object hangs from since this configuration will result in zero net torque.

[@arpitchaudhary5524]

Thank you maam

[@ricardoabh3242]

The diagonal match must be equal or greater in length?

[@Prof-Hafner]

The matches were all the same. Dr. Mayer is the expert, but I think how long the diagonal match needs to be just depends on what angle in the strings is set by the first match.

[@origionalcatastrophe]

That is the incorrect explanation. It needs to stated the bottle is creating a down force but that force is countered by the vertical match being held by the match splitting the string.

[@chounoki]

You totally explained it wrong. The key is that the 3rd match slightly pushes the string, bending it towards the table. As a result, the center of the weight of the entire thing moves slightly left from the edge of the table onto the table, so that it won't fall.

[@chrisreyes8182]

If you have a time machine and go back through time like roman empire time or pompiie is about to go boom boom and show this trick ha your head might end up ina bucket or burn you alive and acuse you for witch craft 😆

[@Prof-Hafner]

I'd take that over living without indoor plumbing! :)

[@chrisreyes8182]

@@Prof-Hafner dont worry my old friend il protect at all cost 😅 would you show this explaination to leonardo if ever we can go back or he probly knows this?

[@jayeisenhardt1337]

@@Prof-Hafner Isn't the Roman Empire what made indoor plumbing a thing?

[@Taricus]

@@jayeisenhardt1337 lol they did have indoor plumbing :P That's what the aquaducts were for. It used physics to create the water pressure, by taking the water from somewhere high and using raised platforms to keep it high above the ground before reaching the city (just like how we use water towers). Gravity makes it work without electricity or pumps.

[@อนุพงศ์ก้อนคํา-ด3ฏ]

มาจากไทยนะคับ55

[@Prof-Hafner]

Welcome!

[@thewanderer1246]

Aint this fake

[@Prof-Hafner]

No. And if you don’t believe me there are about 10,000 YT videos on it by now. 😂

[@jjborenfff]

What's stupid about this?

[@Prof-Hafner]

Actually I agree that one is not so stupid. But if you peruse the entire playlist, I think you will find that many of them are: kzbin.info/aero/PL9_sR6QqqcymqSt5BuprSZLeDjdsNpHAH

[@Tecnotronics223]

All what she said its an explanation by mind.... But before this experiment.. She didn't create this Experiment ....by the same logic... This only explanation.... But explanation can't creat facts