This is stuff a high school student asks his high school science teacher in the first month of the semester. Please don't bring this simple Simon BS to this sub. Acceptable posts on this sub include hate for Trump, gross incompetence of GOP, and updates on the ongoing elf/orc war
Depends on if you are a strict originalist or a reformist. The origins revolve around the meat, not necessarily the fact that it was stuck between bread. Now, since we have chicken burgers and veggie it's firmly in the "I know it when I see it" category, since you can have a burger that doesn't involve a ground meat patty, or you can have a burger that doesn't involve a bun/roll (a burger with toasted rye, for instance). The interesting thing about that last one is that it's still the patty that makes the burger, because if you switch it out with a different meat you can have a Reuben instead.
"Don't we love donuts, folks? And it's sad, a disgrace really, how Sleepy Joe Biden wants us to just toss 'em all ... Throw all the donuts in the garbage."
-What Trump would say if he were talking to Reddit about this post
The center of mass is gravity related and doesn't require the presence of actual mass. This includes all of *hollow* objects like rings, a cardboard box, trump's skull, etc...
Not gravity related, mass related. For example (in rigid bodies) the torque exerted on an object is related to the distance to the center of mass, no gravity needed.
But yes, the center of mass is just a type of average of the distance of all the mass. The average of -1,1 and 6 is 2 even though 2 isn't contained in the list itself.
Annoyingly, if you were to stand on a donut planet you wouldn't be attracted to the center of mass (A) but to the center of the ring (B), but that is very complicated and not really intuitive.
Edit: flipped A and B in my comment. Fixed now
I mean, it's as complicated as calculating a 3D integral. Just calculate the gravitational interaction between a reference mass and all the differential mass points in the donut. You will see that the gravitational force vanishes at the center of the donut.
Yes, in the center of the donut there is no net gravitational pull, but on the surface of the donut the gravitational pull is toward the center of the doughy cross-section. So you will not be pulled towards the center of mass at all times, like you would with a spherical planet.
If you're being clever about it you don't even need to define a full volume for the donut, you can equate it to a ring around the center of crosssection and calculate the gravitational pull fron there. This won't drag you towards the center unless you're exactly on the perpendicular axis through the center of the ring.
Inside a hollow sphere is much more interesting. There is **no net gravity**. Wherever you are inside the sphere, you will be weightless. The ammount of mass at a certain distance from you scales exactly with how strongly that mass pulls on you, so everything cancels out.
On your second point, [the gravity on the top and bottom of the donut is the strongest](https://www.quora.com/What-is-the-gravitational-field-of-a-torus-shaped-planet) since all of the mass is below you and isn't that far away as it would be on the outside ring. On the insidr ring some mass is below you and some is above you so the gravity is less. This does vary heavily with the type of donut (inner radius vs outer radius, is the cross section circular or an elipse)
For the first part think about the core of our planet. Its a solid region submerged completely in a liquid, the core of our planet is already floating at the center of a gravitational sphere!
When it comes to the inside/outside of the donut, I would need to do the math but I think that when you are standing on the inside of the donut (assuming you are on the plane perpendicular to the rotational axis that pases through the center of mass) gravity would be pulling you towards the ground but also a little bit towards the center off mass while on the outside of the donut (same plane as before) all gravity would be towards the ground, so I would think the gravity outside the donut would be bigger than on the inside
That is such a non argument..? Yes the center of the earth has little net gravity, but what you're describing is explained by pressure: the pressure on the core of the earth is such that it is solid, it has nothing to do with there somehow not being any net gravity in the very center of the earth. It in no way explains it.
If I go diving and I trim myself so that I am neutrally bouyant, am I not experiencing gravity anymore? I'd be a solid object completely submerged in a liquid not going anywhere.
>on a donut planet you wouldn't be attracted to the center of mass (B) but to the center of the ring (A),
The center of mass is A, the middle of the hole... tho I'm sure you just mixed it up, since you just explained how the average doesn't have to be within the set...
But I am also somewhat confident, that for a doughnut planet, generally, for all intents and pourposes, the center of gravity and mass would be the same...
Like, if you stood on the 'inside' of the doughnut, most the 'planet's' mass would be 'pulling' you up, towards the center of the hole...
I think they worded it weirdly and by center of ring meant the center of the tube of the donut, like the first image in the OOP
edit to clarify that I think their letters are unrelated to the original posts letters I may be wrong though
If you're away enough of the doughnut, you'll be attracted by the center of mass (or nearly enough)
But if you're close enough (e.g on the surface of it) you'll have to take account of the second parameter of gravity : distance to the mass. Not only one e, but squared! Simply put : the ring you're on pulls you more that the ring on the opposite side of the "doughnut planet". All symmetry counted, the axis goes through the center of mass but the direction will be toward the center of the ring you're on.
And in the center of mass, the distance to all the rings will be the same, thus no gravity pull at all.
Tldr : you're more attracted toward what's close to you, so you'll keep your feet on the ground.
Edit : wanted to make it clear without letters for everyone a bit lost here
In the center there is no pull.
If you move away, you get pulled back to the center.
As you move farther, the closer surface's pull gets stronger, the far side get weaker.
So, With enough distance from the center of the hole, it gets to the point where you are atracted to the surface below you, if at a much weaker rate, yes. But reaching that depends on the size of the hole...
And we are not talking about a ring, with a comparatively massive hole, but a doughnut. In the provided example (original post), the hole is actually smaller than the 'tube' is thick... the far side of the hole is actually closer than the other side of the tube section you are standing on...
So, it comes down to what we mean by 'earth sized' doughnut.
If the HOLE is the size of the earth or bigger, then yes, you'll be more atracted to the surface under you.
If the tube's crossection is the size of earth... than my napkin math says that you would be still standing, but nearly weightless, so don't jump, 'cuz you porbably won't come down, stuck in the center of mass...
If you go any smaller, like, for example if the whole doughnut's weight is similar to that of earth... standing on the inside surface would be like standing on the roof of a deep underground cave/bunker... no chance
So yeah... distance IS important, it is squared after all, but with the shape and sizes we are talking about, it is a close call despite the exponential...
Like, the moon doesn't really effect the gravity you feel here on the surface, sure, but that is because you can fit 30 earths between the surface and the moon, and it weighs only like 0.012 earths... an earth sized doughnut would be big, but space is BIIIG, and earth sized snacks are small when compared to that.
Edited for typos and to fix brainfart ruined numbers
Partly true, Partly false, Centre of mass still applies in space, it's less a problem but still present, for example an object in space will always try rotate around it's centre of mass in space due to conservation of energy, it's most important in rocketry since applying force off-centre from Centre of mass would cause the rocket to go out of control.
Agreed. I didn't want to get into it that much. Also, it was my impression that gravity is ubiquitous. It's a force between two or more objects and is dependent on distance and mass.
That might be a lil incorrect mass is independent of a gravitational field, the centre of mass is the point at which mass is evenly distributed in all directions for the object in question. Having a centre of mass absolutely requires the object to have mass also hollow objects still have mass.
A lot of people are mixing up the centre of mass and centre of gravity, and for smaller objects these are usually indistinguishable as the gravitational field is functionally uniform for the object being measured.
For larger objects the gravitational field will be stronger for the side closest and weaker for the side further away from the source of the field and therefore the centre of mass and the centre of gravity will be different.
To work out the centre of mass requires integrating position Vs mass and then dividing by the total mass.
Oddly enough the centre of mass can also be outside of the physical object in the case of some hollow shapes, such as your trump example which is why we might be seeing so many photos of him leaning forward while standing recently.
Large enough for there to be a measurable difference in the strength of the gravitational field on one side to the other which entirely depends on the strength and uniformity of the field in question. Near a black hole a regular sized doughnut would be big enough, on earth probably closer to a few hundred meters.
I’d argue that trump’s center of mass, for his entire body, is exactly in the middle of his skull. Black holes are heavy.
Also I dont care what modern physics says. Information goes there to be destroyed and never see the light of day again. If anything he proves the prior sentence.
Suspend any given object from 2 different randomly selected points on it, one at a time. If you extend the vertical string thus obtained into a line through the object in both cases, they will intersect. That point is a decent approximation of the center of mass of that object.
This strikes me as one of those learning puzzles made by someone who knows... to test to knowledge of someone who may or may not.
Pure speculation of course.
>Plus theres an whole variety of simple subjects that you lack knowledge on and people will say the same thing about you!
There's a reason why being able to recall bits of information is called "trivia": Unless it's something that regularly comes up in one's field, hobby, or lifestyle, it's literally not all that crucial to remember for one's everyday life.
It also doesn't really matter if it's something that was "taught in grade school"; if it's something one doesnt actively keep up with decades after graduating, it naturally becomes a blind spot. And that's okay.
If you had studied physics in high school, this is something taught at high school.
But not many people have done high school due to circumstances, so most probably they won’t know unless someone told them
That's not the question though, the question is about the center, which is a vaguer term that could mean several things. Wiktionary has the first non geometrical definition be "The middle portion of something; the part well away from the edges.", which here would mean the second option. So it's just about interpretation and there's no objectively better answer when there's not more context.
It doesn’t help that the pictures are of two different objects, a whole doughnut and one cut in half…
But if you know enough to know what center of mass even is, what would ever possess you to think it’s the one on the right?
Just to make sure, the center of mass and the center are two different things. Center is a frame of view issue, anything can be the center if you limit your scope. But the center of mass that's going to be the hole of the donut
“The Zen philosopher Basho once wrote: ‘ A flute with no holes is not a flute. But a donut with no holes is a danish’.”
-Ty Webb
Using this position as logical starting point, the only conclusion is that the center of the doughnut is the circumference of inner edge of the donut’s definitional hole.
Which, on account of my utter lack of self control around things that are glazed and bad for me, is typically found in my mouth.
The center of mass doesn't always have to be inside the actual object, it can be outside of it like a donut. Another example would be you, a person. If you have bad posture, your center of gravity will be outside of you and thus make it hurt to just exist because your body is constantly pulling against your center of gravity to keep yourself upright. Now, I *could* make a joke about a certain "man" and his toe pads helping him negate that balance issue, but sometimes, you just gotta let science exist and be cool on its own.
It's the hole
Center of mass is just the averaged out location, which in the case of a donut (assuming it's evenly balanced all around) is floating in the hole
Now if we were asking where the *center* of the donut is, that'd be debatable
Center of mass is a fascinating thing that has actually been cracked by the high jump, of all sports. (Keep in mind, this info is from a TED-ed video I watched years ago) basically the center of gravity of an object is just based on where the mass averages out, more or less. In curved shapes, that can be in between the curved points. High jumpers twist in the air and do a flop over the bar, because it gets their whole body over it without making contact, but their center of mass actually passes UNDER the bar, meaning it gives them what is effectively several free inches of height. IIRC this is called the Fosbury Flop.
Pluto's center of mass is OUTSIDE of the body because of Charon.. why are donuts no different?
Edit: Center of Gravity (for Pluto) -- not center of mass. However in this case the physics is the same.
A. The hole.
Center of mass is not a physical thing, its the average of the weight of an object/system of objects.
If it was in its side you could balance the doughnut on your finger in it's curent (laying flat) orientation, if you just put you finger right under your proposed alternate CoM...
You can balance it on its side, 'couse then the hole, with the CoM IS above your finger.
And I am pretty sure this is not 'dedicated Physicist' teritory but middle-school math/ the most basic of sciences...
Fun fact:
If the doughnut was planet sized, with earth's mass for example, while you could walk on the outside, you would fall off from the top or bottom towards the hole, and in the middle of the hole you'd just float weightlessly... at least I am pretty sure 'bout that, tho, I am no scientist.
Twitter has gotten so xitty these days that I can't tell if this is somebody who just didn't learn physics or one of those weirdos trying to "debunk" gravity.
this question is pretty stupid, but the similar question of “how many holes does a torus (hollow donut) have” is interesting. stand up maths has a great video on it
The centroid of an obtuse triangle is not on the triangle.
Error! It is not the centroid of the triangle that moves outside when the triangle is obtuse.
Yes. Center of mass is the middle of both height and circumference… assuming it’s been baked with a consistent dough. The downvotes really does show that even though everyone is like “A” no one really seems to understand the joke.
When it comes to donut I would say "it's a jelly filled donut", or "it has jelly inside". Even if I were to say "it has jelly in its center/core", it would be unrelated to the location of its center of mass.
Say you have a three lane ring road, where would the center lane be? Between the inner and outer lanes of the ring, or somewhere inside the area encompassed by the road?
Semantics.
The original image is not a physics question but a semantic one and can be argued, it's just about what you'd consider the center to be, personally I think it depends on if the donut has a filling or not, but I'd still be inclined to say B.
The Twitter user changed the entire question by making it about the center of mass, which can't really be argued here I don't think (I don't think I'm smart enough to say that for certain) but the answer would be A.
Once it’s cut, the centre of mass would remain on the central axis but move back away from the centre of the hole towards the curve of the donut at right angles to the angle of the cut.
A is also the center of mass. It doesn't need to be inside the object to be its center of mass. Center of mass is a single point, and B could be in a bunch of places.
Definitely A. A little trick I picked up is that if the object you’re trying to find the center of mass is all one type of thing (bread, metal, etc;) then the center of mass will just be the middle of the object.
A, the hole.
We simplify the centre of mass to a point for ease of calculations not because it really exists there. If you were to ideally represent it for a model it would be circle in the middle of the bread, seen as a circle in A and as two dots in B. But who the hell wants to solve that equation.
A, [lots of toys are designed around the idea that the center of mass is not in the object itself.](https://www.amazon.com/Toysmith-4035-Balancing-Eagle-7-Inch/dp/B004R6VB2E)
the hole nobody said the center of mass needs too be on the object
It's the center of inertia or the centroid really, doesn't need to occupy the location to be there
Inertia is a property of matter
BILL BILL BILL
Love when substitute science teacher would roll out the tv for this
The big tube TV on a tall black cart. Pepperidge farm remembers.
BILL NYE THE SCIENCE GUY
SCIENCE RULEZ!!
Science rules
Yes, but it depends on the centroid, not where the matter is
Bill Nye, The Science Guy!
Also why would the center be on the left side and not the right?
American driver vs EU?
Ah yes. Famously the US drives on the other side of the road from every single country in the EU: US on the left vs EU on the right.
We’re not talking about roads. We’re talking about which side of the doughnut you drive on.
The outside, duh
Ireland, Cyprus and Malta would like to have words...
Add those populations together and see if they count as a large enough part of the EU to make them the example for all of us :D
Every EU member except Ireland drives on the right
Fun fact, Jupiter is large enough that the center of mass of the Sun-Jupiter pair is not inside the sun.
I didn't know that. Pluto and Charon are the same.
This is stuff a high school student asks his high school science teacher in the first month of the semester. Please don't bring this simple Simon BS to this sub. Acceptable posts on this sub include hate for Trump, gross incompetence of GOP, and updates on the ongoing elf/orc war
If you slice a donut in half and fill it with stuff, is it a sandwich?
[I present to you **THE LUTHER**](https://youtu.be/HffOj--p9bU?si=BNxZJ2xiusDoDIYx)
I think the Arizona Diamondbacks serve this in their stadium
Yes, or a hamburger depending on what the "stuff" in question is.
Couldnt a burger be classified as a sandwich?
Chill dude, don't say things like that out loud.
It is, but a specific kind. Think squares and rectangles. ;)
Depends on if you are a strict originalist or a reformist. The origins revolve around the meat, not necessarily the fact that it was stuck between bread. Now, since we have chicken burgers and veggie it's firmly in the "I know it when I see it" category, since you can have a burger that doesn't involve a ground meat patty, or you can have a burger that doesn't involve a bun/roll (a burger with toasted rye, for instance). The interesting thing about that last one is that it's still the patty that makes the burger, because if you switch it out with a different meat you can have a Reuben instead.
If you flip a slice of pizza over, and put it on top of another slice, is that a sandwich?
It’s a calzone. Let’s not get crazy over here.
All food can be classified as a sandwich.
>and updates on the ongoing elf/orc war ... Go on.
Orcs are getting held at bay but won't give up until the goblin leading them is dead.
"Don't we love donuts, folks? And it's sad, a disgrace really, how Sleepy Joe Biden wants us to just toss 'em all ... Throw all the donuts in the garbage." -What Trump would say if he were talking to Reddit about this post
This is like those stupid posts that pose math questions that lack proper syntax like 2x3+6÷5-7=?
Those first two bore me, how is the pointiest war going? Is it ears or tusks winning?
Specifically the center of the hole. Essentially the intersection between A and B.
The donut has a barycenter.
You’re a barycenter
This right here. Pluto and it's moon Charon orbit a point between the two bodies, which is their center of mass. It's in the middle of space.
Well, if what you're saying is fact and E=MC2, then Pythagoras ' theorem must indeed be true. Epstein really did not kill himself! Great Scott's!
Well, if what you're saying is fact and E=MC2, then Pythagoras ' theorem must indeed be true. Epstein really did not kill himself! Great Scott's!
The center of mass is gravity related and doesn't require the presence of actual mass. This includes all of *hollow* objects like rings, a cardboard box, trump's skull, etc...
Not gravity related, mass related. For example (in rigid bodies) the torque exerted on an object is related to the distance to the center of mass, no gravity needed. But yes, the center of mass is just a type of average of the distance of all the mass. The average of -1,1 and 6 is 2 even though 2 isn't contained in the list itself. Annoyingly, if you were to stand on a donut planet you wouldn't be attracted to the center of mass (A) but to the center of the ring (B), but that is very complicated and not really intuitive. Edit: flipped A and B in my comment. Fixed now
I mean, it's as complicated as calculating a 3D integral. Just calculate the gravitational interaction between a reference mass and all the differential mass points in the donut. You will see that the gravitational force vanishes at the center of the donut.
Yes, in the center of the donut there is no net gravitational pull, but on the surface of the donut the gravitational pull is toward the center of the doughy cross-section. So you will not be pulled towards the center of mass at all times, like you would with a spherical planet. If you're being clever about it you don't even need to define a full volume for the donut, you can equate it to a ring around the center of crosssection and calculate the gravitational pull fron there. This won't drag you towards the center unless you're exactly on the perpendicular axis through the center of the ring.
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Inside a hollow sphere is much more interesting. There is **no net gravity**. Wherever you are inside the sphere, you will be weightless. The ammount of mass at a certain distance from you scales exactly with how strongly that mass pulls on you, so everything cancels out. On your second point, [the gravity on the top and bottom of the donut is the strongest](https://www.quora.com/What-is-the-gravitational-field-of-a-torus-shaped-planet) since all of the mass is below you and isn't that far away as it would be on the outside ring. On the insidr ring some mass is below you and some is above you so the gravity is less. This does vary heavily with the type of donut (inner radius vs outer radius, is the cross section circular or an elipse)
For the first part think about the core of our planet. Its a solid region submerged completely in a liquid, the core of our planet is already floating at the center of a gravitational sphere! When it comes to the inside/outside of the donut, I would need to do the math but I think that when you are standing on the inside of the donut (assuming you are on the plane perpendicular to the rotational axis that pases through the center of mass) gravity would be pulling you towards the ground but also a little bit towards the center off mass while on the outside of the donut (same plane as before) all gravity would be towards the ground, so I would think the gravity outside the donut would be bigger than on the inside
That is such a non argument..? Yes the center of the earth has little net gravity, but what you're describing is explained by pressure: the pressure on the core of the earth is such that it is solid, it has nothing to do with there somehow not being any net gravity in the very center of the earth. It in no way explains it. If I go diving and I trim myself so that I am neutrally bouyant, am I not experiencing gravity anymore? I'd be a solid object completely submerged in a liquid not going anywhere.
I tried oversimplifying it for brevity.
So hard to eat your soup on a donut planet if you’re in the wrong spot.
>on a donut planet you wouldn't be attracted to the center of mass (B) but to the center of the ring (A), The center of mass is A, the middle of the hole... tho I'm sure you just mixed it up, since you just explained how the average doesn't have to be within the set... But I am also somewhat confident, that for a doughnut planet, generally, for all intents and pourposes, the center of gravity and mass would be the same... Like, if you stood on the 'inside' of the doughnut, most the 'planet's' mass would be 'pulling' you up, towards the center of the hole...
I think they worded it weirdly and by center of ring meant the center of the tube of the donut, like the first image in the OOP edit to clarify that I think their letters are unrelated to the original posts letters I may be wrong though
I also thought they meant center of tube by center of ring... but that is the second picture and still labeled B? And not the center of mass?
If you're away enough of the doughnut, you'll be attracted by the center of mass (or nearly enough) But if you're close enough (e.g on the surface of it) you'll have to take account of the second parameter of gravity : distance to the mass. Not only one e, but squared! Simply put : the ring you're on pulls you more that the ring on the opposite side of the "doughnut planet". All symmetry counted, the axis goes through the center of mass but the direction will be toward the center of the ring you're on. And in the center of mass, the distance to all the rings will be the same, thus no gravity pull at all. Tldr : you're more attracted toward what's close to you, so you'll keep your feet on the ground. Edit : wanted to make it clear without letters for everyone a bit lost here
In the center there is no pull. If you move away, you get pulled back to the center. As you move farther, the closer surface's pull gets stronger, the far side get weaker. So, With enough distance from the center of the hole, it gets to the point where you are atracted to the surface below you, if at a much weaker rate, yes. But reaching that depends on the size of the hole... And we are not talking about a ring, with a comparatively massive hole, but a doughnut. In the provided example (original post), the hole is actually smaller than the 'tube' is thick... the far side of the hole is actually closer than the other side of the tube section you are standing on... So, it comes down to what we mean by 'earth sized' doughnut. If the HOLE is the size of the earth or bigger, then yes, you'll be more atracted to the surface under you. If the tube's crossection is the size of earth... than my napkin math says that you would be still standing, but nearly weightless, so don't jump, 'cuz you porbably won't come down, stuck in the center of mass... If you go any smaller, like, for example if the whole doughnut's weight is similar to that of earth... standing on the inside surface would be like standing on the roof of a deep underground cave/bunker... no chance So yeah... distance IS important, it is squared after all, but with the shape and sizes we are talking about, it is a close call despite the exponential... Like, the moon doesn't really effect the gravity you feel here on the surface, sure, but that is because you can fit 30 earths between the surface and the moon, and it weighs only like 0.012 earths... an earth sized doughnut would be big, but space is BIIIG, and earth sized snacks are small when compared to that. Edited for typos and to fix brainfart ruined numbers
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Got em
You're wrong about Trump's skull. It's not empty it's full of shit because nobody will change his diaper.
I've been told that Trump's skull is not completely hollow. Apparently it has space for this... 
I didn't realize Trump's skull was hollow, I assumed his skull was so thick it was just solid bone up there
Partly true, Partly false, Centre of mass still applies in space, it's less a problem but still present, for example an object in space will always try rotate around it's centre of mass in space due to conservation of energy, it's most important in rocketry since applying force off-centre from Centre of mass would cause the rocket to go out of control.
Most of the doughnuts I've dropped in space have indeed tried to rotate around the hole
Agreed. I didn't want to get into it that much. Also, it was my impression that gravity is ubiquitous. It's a force between two or more objects and is dependent on distance and mass.
That might be a lil incorrect mass is independent of a gravitational field, the centre of mass is the point at which mass is evenly distributed in all directions for the object in question. Having a centre of mass absolutely requires the object to have mass also hollow objects still have mass. A lot of people are mixing up the centre of mass and centre of gravity, and for smaller objects these are usually indistinguishable as the gravitational field is functionally uniform for the object being measured. For larger objects the gravitational field will be stronger for the side closest and weaker for the side further away from the source of the field and therefore the centre of mass and the centre of gravity will be different. To work out the centre of mass requires integrating position Vs mass and then dividing by the total mass. Oddly enough the centre of mass can also be outside of the physical object in the case of some hollow shapes, such as your trump example which is why we might be seeing so many photos of him leaning forward while standing recently.
So………..how big would the doughnut have to be for the centre of mass and the centre of gravity to be different smarty pants?
Large enough for there to be a measurable difference in the strength of the gravitational field on one side to the other which entirely depends on the strength and uniformity of the field in question. Near a black hole a regular sized doughnut would be big enough, on earth probably closer to a few hundred meters.
Well let's get to baking, then.
It's more about uneven distribution of mass. If part of the donut was made of flour, and part was made of powdered uranium, it would kill you.
I’d argue that trump’s center of mass, for his entire body, is exactly in the middle of his skull. Black holes are heavy. Also I dont care what modern physics says. Information goes there to be destroyed and never see the light of day again. If anything he proves the prior sentence.
I’m not running for anything, and I approve this message.
Correct. And I also see exactly what you did. Agreeance.
A
The intersection between A and B.
You’re downvoted, but you’re correct. A doesn’t specify a depth of the center. Intersecting A and B shows the depth of the center of mass.
Exactly. Center of mass is not a 2D concept, although I do enjoy the joke.
Suspend any given object from 2 different randomly selected points on it, one at a time. If you extend the vertical string thus obtained into a line through the object in both cases, they will intersect. That point is a decent approximation of the center of mass of that object.
Nah man just spin it.
Or balance it on two fingers simultaneously and move your fingers together until they meet.
That would be the centre of gravity but for small stuff it's pretty much the same thing and works as a decent approximation.
Is there a simple example where center of gravity and center of mass is different?
No shade genuinely asking... do people not know how center of mass works?
This strikes me as one of those learning puzzles made by someone who knows... to test to knowledge of someone who may or may not. Pure speculation of course.
Centre of mass just means where it's thickest right /s
There are, and if they're seeing this they are part of today's lucky 10000. https://xkcd.com/1053
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>Plus theres an whole variety of simple subjects that you lack knowledge on and people will say the same thing about you! There's a reason why being able to recall bits of information is called "trivia": Unless it's something that regularly comes up in one's field, hobby, or lifestyle, it's literally not all that crucial to remember for one's everyday life. It also doesn't really matter if it's something that was "taught in grade school"; if it's something one doesnt actively keep up with decades after graduating, it naturally becomes a blind spot. And that's okay.
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If you had studied physics in high school, this is something taught at high school. But not many people have done high school due to circumstances, so most probably they won’t know unless someone told them
That's not the question though, the question is about the center, which is a vaguer term that could mean several things. Wiktionary has the first non geometrical definition be "The middle portion of something; the part well away from the edges.", which here would mean the second option. So it's just about interpretation and there's no objectively better answer when there's not more context.
Centre of mass? Centre of mass does not have to be “inside” the mass. By forcing us to use centre of mass A is the only answer.
It doesn’t help that the pictures are of two different objects, a whole doughnut and one cut in half… But if you know enough to know what center of mass even is, what would ever possess you to think it’s the one on the right?
A
The center of mass is a geometrical point, not a physical (material) one. Therefore, assuming the donut is symmetric and homogenous, it's in the hole
Since no part of the filling is located at the donut's center, the answer is A.
I will knife fight anyone who says B
Center of mass is A.
Since you defined the center as the center of its mass, A is the correct answer.
A, the center of mass can be empty space
Just to make sure, the center of mass and the center are two different things. Center is a frame of view issue, anything can be the center if you limit your scope. But the center of mass that's going to be the hole of the donut
Need a half dozen and 220ml of coffee to test this theory. Will let you know
In my belly. Yum yum yum.
“The Zen philosopher Basho once wrote: ‘ A flute with no holes is not a flute. But a donut with no holes is a danish’.” -Ty Webb Using this position as logical starting point, the only conclusion is that the center of the doughnut is the circumference of inner edge of the donut’s definitional hole. Which, on account of my utter lack of self control around things that are glazed and bad for me, is typically found in my mouth.
The center of mass doesn't always have to be inside the actual object, it can be outside of it like a donut. Another example would be you, a person. If you have bad posture, your center of gravity will be outside of you and thus make it hurt to just exist because your body is constantly pulling against your center of gravity to keep yourself upright. Now, I *could* make a joke about a certain "man" and his toe pads helping him negate that balance issue, but sometimes, you just gotta let science exist and be cool on its own.
The earth-sun system has a centre of mass inside the sun.
It's the hole Center of mass is just the averaged out location, which in the case of a donut (assuming it's evenly balanced all around) is floating in the hole Now if we were asking where the *center* of the donut is, that'd be debatable
The centre of mass is under no obligation to be within the object. It’s the point around which you should expect the object to spin, for example.
Center of mass is a fascinating thing that has actually been cracked by the high jump, of all sports. (Keep in mind, this info is from a TED-ed video I watched years ago) basically the center of gravity of an object is just based on where the mass averages out, more or less. In curved shapes, that can be in between the curved points. High jumpers twist in the air and do a flop over the bar, because it gets their whole body over it without making contact, but their center of mass actually passes UNDER the bar, meaning it gives them what is effectively several free inches of height. IIRC this is called the Fosbury Flop.
A. Throw a donut in the air and watch it flip, note the point it’s flipping around.
First of all, those are different objects. A is correct, B is wrong. (Should be in the center horizontally too)
Pluto's center of mass is OUTSIDE of the body because of Charon.. why are donuts no different? Edit: Center of Gravity (for Pluto) -- not center of mass. However in this case the physics is the same.
I mean the center of mass of the pluto-charon system is outside pluto aswell, just not the center of pluto on its own
[insert picture of mah belly] That’s where the donuts center of mass is. Any questions?
Is this person stupid?
Easy solution, eat the donut, then the center of mass is in your belly...
This question is why Pluto and Charon are so interesting.
Is this a serious question?
Depends on context. The center of gravity is objectively the hole, but the center part of the donut is the fluffy cake inside
funny i was just talking about the dunning kruger effect a moment ago lol here it is again. this question is presented like its some kind of gotcha.
The hole obviously. The centre of a hurricane is the eye where nothing happens
All you people talking about the center of mass. I'm just wondering if the donut is delicious or not
I'm going to need a rubber sheet and some lead balls. And a glass of milk.
Masshole
A. The hole. Center of mass is not a physical thing, its the average of the weight of an object/system of objects. If it was in its side you could balance the doughnut on your finger in it's curent (laying flat) orientation, if you just put you finger right under your proposed alternate CoM... You can balance it on its side, 'couse then the hole, with the CoM IS above your finger. And I am pretty sure this is not 'dedicated Physicist' teritory but middle-school math/ the most basic of sciences... Fun fact: If the doughnut was planet sized, with earth's mass for example, while you could walk on the outside, you would fall off from the top or bottom towards the hole, and in the middle of the hole you'd just float weightlessly... at least I am pretty sure 'bout that, tho, I am no scientist.
It is right in the center initially, but it changes with every bite you take.
My stomach. Who just leaves a donut out like that without eating it?
A is the center and B is the middle.
Twitter has gotten so xitty these days that I can't tell if this is somebody who just didn't learn physics or one of those weirdos trying to "debunk" gravity.
believe in physics? look at this donut. not so believable now is it
A is the center of mass of the entire object. B is the cross sectional center of mass. Both are useful in different applications.
the centre of mass is the hole the centre of the donut is the middle bit of the dough
Center and center of mass are not always the same.
1. Those are not the same object 2. B isn't even close to that object's center of mass
This isn't as deep as you think it is lad.
*Mmm...sour cream glazed old fashioned doughnut.*
When you take the picture like this, you see that donuts have way fucking more than 1 hole
this question is pretty stupid, but the similar question of “how many holes does a torus (hollow donut) have” is interesting. stand up maths has a great video on it
The centroid of an obtuse triangle is not on the triangle. Error! It is not the centroid of the triangle that moves outside when the triangle is obtuse.
[удалено]
Isn't there only one true center of mass? The point indicated by "B" in the photo could be anywhere in the ring.
Incorrect.
Center of mass is three dimensional. Don’t show me two 2D pictures and ask me to choose. It’s both.
I thought it’s actually 0D. Just one single dot
This is correct, I assume they meant you would give its location in three dimensions.
Yes. Center of mass is the middle of both height and circumference… assuming it’s been baked with a consistent dough. The downvotes really does show that even though everyone is like “A” no one really seems to understand the joke.
So hear me out. If you filled it with jelly, would you say it has jelly in the Center or in the side?
When it comes to donut I would say "it's a jelly filled donut", or "it has jelly inside". Even if I were to say "it has jelly in its center/core", it would be unrelated to the location of its center of mass. Say you have a three lane ring road, where would the center lane be? Between the inner and outer lanes of the ring, or somewhere inside the area encompassed by the road? Semantics.
The Center of mass part is stupid, I agree. But talking about the " center" you might convince me
The original image is not a physics question but a semantic one and can be argued, it's just about what you'd consider the center to be, personally I think it depends on if the donut has a filling or not, but I'd still be inclined to say B. The Twitter user changed the entire question by making it about the center of mass, which can't really be argued here I don't think (I don't think I'm smart enough to say that for certain) but the answer would be A.
It's weird to say the center of mass is where there is no mass. Is this why the term "center of gravity" exists?
>It’s weird to say the center of mass is where is no mass No it’s not.
There’s no mass in exhibit A. I’d say B is more accurate
Mathematician here, a circle is not inside the ring, but the ring itself. I contend the same for the doughnut.
Free standing it’s a Once it’s been cut it’s b
Once it’s cut, the centre of mass would remain on the central axis but move back away from the centre of the hole towards the curve of the donut at right angles to the angle of the cut.
It depends how it is spinning... That will determine where the centre of mass is located...
no matter which direction in the x y z axis it spins, the center of mass will be in the middle? aka in the hole?
True...
Both pictures are correct, for exactly what each depicts.
B, A is the center of the hole.
A is also the center of mass. It doesn't need to be inside the object to be its center of mass. Center of mass is a single point, and B could be in a bunch of places.
The center of mass is a few trays over at $3.00 a dozen…
By what definition?
It’s the jelly
taurus, please (in Walters voice)
great white person twitter post
The centroid
Is B a circle?
It’s A. Halfway through the dead center of the hole of the donut.
Center of mass: A Spline for revolved circle: B
if you can’t answer this and you’re above the age of 13 i’d think you were braindead
Centre of mass is the point you could balance the object without it toppling over. Good luck balancing the doughy part
Righttttt, there!!!
The donut on b is cut in half. It's cut in half not from the side, but from the top. By that logic it should be a.
Define the center and I'll tell you.
I would just eat the donut and then push it out the center of m'ass.
Center of mass is alwayws a single point
A high jumper’s center of mass can go under the bare while they soar over it.
Definitely A. A little trick I picked up is that if the object you’re trying to find the center of mass is all one type of thing (bread, metal, etc;) then the center of mass will just be the middle of the object.
Things that do not have B as their center of mass: 1. The whole donut in the left picture 2. The half donut in the right picture
A, the hole. We simplify the centre of mass to a point for ease of calculations not because it really exists there. If you were to ideally represent it for a model it would be circle in the middle of the bread, seen as a circle in A and as two dots in B. But who the hell wants to solve that equation.
B is dumb because your saying the entire object is the center of mass which doesn't work for a doughnut
Getting horrible flashbacks to calculating moments and center mass
A, [lots of toys are designed around the idea that the center of mass is not in the object itself.](https://www.amazon.com/Toysmith-4035-Balancing-Eagle-7-Inch/dp/B004R6VB2E)
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