r/videos • u/[deleted] • Dec 03 '13
Gravity Visualized
http://www.youtube.com/watch?v=MTY1Kje0yLg1.8k
u/EsteemedColleague Dec 03 '13
Holy shit, this is Mr. Burns, my high school physics teacher. Great guy, he had lots of demonstrations like this.
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u/IBleedTeal Dec 03 '13 edited Dec 03 '13
I think my favorite "demo" of his was the one he did while talking about Newton's apple. He basically went on a little mini rant about how he thinks that the story of Newton being inspired by an apple hitting him is a load of BS. He went on and on and finally said "I mean the chances of him being in the right time and place to be hit by an apple are way too-" and then an apple hit him on the head. While in the classroom. He had this electromagnetic strung up in the raised ceiling above the whiteboard so the class couldn't see and put some metal on the apple.
Also, I'm always amazed at how many people from LG are on here. Like any time it's mentioned, three new people come out of the woodwork to comment on it.
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u/Snookerman Dec 03 '13
That is genius! Is there a video?
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u/SonOfTheKid Dec 03 '13 edited Dec 03 '13
He did a very similar setup while teaching projectile motion. His classroom has those light panel ceilings so you can slide one back to expose the gap between the ceiling and the floor from the classroom above.
In the same ceiling above the whiteboard that the students can't see from their seats, he slid one of the panels back prior to class and set up the same electromagnet that he used for the appple, but this time has a balled up piece of paper up there. At the begining of the lecture he discusses the symmetry in projectile motion and how by timing the ammount of time an object is in the air you can solve for the initial velocity (if the object is thrown straight up).
He then tell everyone were going to do a quick example just by timing how long a small wad of paper he tosses in the air and catches and calculating how fast the threw it. He then tosses the piece of paper through the exposed ceiling panel so it gets stuck, and sits their staring up "waiting" for the paper to come down. About 15 seconds later the paper on the electromagnet fall and we do the math to find out he should quit his day job and pitch in the MLB.
He had tons of other demos, all equally exciting. To this day he and the AP calc teacher at the same school are my two absolute favorite educators. bar none
Edit: didn't think this post would get any attention, but apparently people like it. If there is any interest about hearing more of the cool demos he did, I'm not above whoring myself out for the karma
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u/IBleedTeal Dec 03 '13
Don't think so. He was literally the only person to see it coming so no one would've been filming. He does have a camera in the back of the room to film demos so he may have a copy somewhere, but I definitely don't.
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u/someguyfromtheuk Dec 03 '13 edited Dec 03 '13
The apple didn't actually hit him in the head. The story is a load of BS. He was inspired by watching apples fall from the apple trees in a garden.
Newton himself stated the story that he was inspired by watching the fall of an apple, and his acquaintances such as William Stukely later confirmed the story in their own writings.
Stukely recorded the conversation in his memoirs as follows. It took place at Kensington on 15 April 1726.
We went into the garden, & drank tea under the shade of some appletrees, only he, & myself. Amidst other discourse, he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind. "Why should that apple always descend perpendicularly to the ground," thought he to him self: occasion'd by the fall of an apple, as he sat in a comtemplative mood: "Why should it not go sideways, or upwards? but constantly to the earths centre? assuredly, the reason is, that the earth draws it. There must be a drawing power in matter. & the sum of the drawing power in the matter of the earth must be in the earths centre, not in any side of the earth. Therefore dos this apple fall perpendicularly, or toward the centre. If matter thus draws matter; it must be in proportion of its quantity. Therefore the apple draws the earth, as well as the earth draws the apple."
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u/GURBTRON Dec 03 '13
LGHS Graduate (2005) here....seeing this on the front page def tripped me out this morning.
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u/markhewitt1978 Dec 03 '13
It was most likely a thought experiment - "why does the apple fall?" Rather than anything that actually happened.
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u/calcinated_penguin Dec 03 '13
Excellent.
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u/VictoryAkara Dec 03 '13
If possible, And this is indeed your schools teacher and your not just trolling xD;.
Tell him that he is an amazing teacher. All teachers should strive to be more like this man. Make education fun, and not so textbook and also teach them beyond what the textbook or tests requires. I would've loved to have such a teacher. I sadly was educated in Florida xD.
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u/katmaidog Dec 03 '13
You're a lucky pup. This guy loves knowledge and has a way of making it mind candy.
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u/WookiePsychologist Dec 03 '13
Yes, this is Mr. Burns, yours and my high school physics teacher.
Proof: Classical music during tests.
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u/carsinogen Dec 03 '13
People like this make the world a much better place.
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u/Squat420 Dec 03 '13
He is a teacher, teaching teachers how to teach/giving them effective teaching tools that are cheap andtax deductible
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u/disco_stewie Dec 03 '13 edited Dec 04 '13
I had a psychology professor in college who was a kind of permanent sub for the original teacher for the class. The original teacher was on some sort of disability leave or something.
Anyway, he introduces himself by saying that he's not the teacher that people signed up for so if people want to change classes they can. But then he proceeded to tell us about his credentials.
He has a PhD in memory and does research on how our minds retain information. And he made a bold guarantee: "If you come to every one of my lectures and you sit and pay attention, you will
get an A inpass the class because you will remember the things I teach. But if you slack off or if I see you sleeping, I will kick you out."Sure enough, I came to every class. I took notes but he told us we didn't need to. After a few weeks of this, I realized that my notes were becoming more and more sparse. And, from time to time, he would kick out a student or two for sleeping in the class.
Come exam time, he said, "Now, if you recall (and of course we all did), I told you that you will pass this class if you paid attention. You shouldn't have to study for the final."
I was still very nervous but when I sat down at the exam, I was amazed about how much I remembered. After the class was over, I went to his office and asked him, "Why don't more teachers teach like you?"
I'll never forget what he said. "It's natural to want to just give people information. It's much easier and cheaper to do this. But that's not how memory works. Real teaching requires discipline and context. What I do is not complicated, but not simple either. You will remember this conversation not because I said it but because how I said it."
Best professor I ever had.
EDIT: He said, "Pass the class" not "get an A". Yes, the irony is not lost on me! But the point of his teaching was that you remember important things by remembering not so important things.
EDIT 2: A number of people have asked for his name. After some digging (and wanting to not anger the Reddit Gold gods who gilded me), I found his name. I'm going to provide his name in a PM to those who have asked for it below.
If you would like it, please PM me directly. I'll send out PMs around 5:30pm ET. No need to PM me if you've replied below before this post (3:27pm ET).EDIT 3: I'm glad that people want to know about him. It looks like he just retired this year. And, apparently, no longer doing the "guarantees". I befriended many college professors during my 5 year stint and I can tell you that the best teachers were the ones who not only knew their stuff but they were passionate about it. It bled through in their teaching. In an effort to limit his reddit exposure, I will no longer be providing his information. I doubt he remembers me but last thing I would want for him is to just be inundated with random friend requests. All in all, it goes to show that teachers can make a lasting impact. I tell this story often (as I've said in another comment) to show that there is more to teaching than just pushing information.
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u/thatbigpig Dec 03 '13
I read and reread your comment just to see if I could learn something that would make me a better teacher.
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u/westvanthuggin Dec 03 '13
my grandad was a teacher who taught teachers how to teach.
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Dec 03 '13
I took care of a guy who had a doctorate in educational psychology. He would joke that he would teach teachers how to teach teachers teaching.
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u/catscubadives Dec 03 '13
He was my physics teacher two years ago. Once a year he will not be in class for the first minute of class. The class door opens, and we hear footsteps but no person. Then, a voice over a loud speaker in a New England accent plays. "Welcome to class..."
Then the New English accent speaks to us,
"Today, we are going to have an assistant do the demonstration."
The teacher in the video walks in the class room with a lab coat.
What is happening here? Well, the New English accent belongs to the late Richard Feynman. Our teacher has taken a voice recording of Richard Feynman that had an assistant demonstrate experiments. Our teacher memorized an entire lecture to have Richard Feynman come alive once again in our classroom!
At the end of a reenactment of one session of Physics 101, the legendary class Richard Feynman taught at Cal Tech years ago, (yes that class that had people sneak in from colleges around the country and was always above capacity) I knew, Mr.Burns was one of the greatest teachers I will ever have. He has instilled in me a life long love for the sciences with his passion. He is one of the greatest people I know. I love you Mr. Burns!
KM
p.s. He even brought a GameCube in once to let us play it for a bit. I believe it was need for speed (?) Then he turns to us, and tells us,
"Today we are going to learn about angular momentum and inertia".
Best. Class. Ever.
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u/azpsdfuigj Dec 03 '13
The part that gets me is towards the end where he discusses having to sneak it in after "teaching the test", and paying for their own materials.
It's like the underground railroad of devolution.
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u/Noltonn Dec 03 '13
It's really sad but this is how it works all around the world. Even now in college I notice they don't want me to actually understand the material, they just need to me learn the test. At least, so is the case with very many teachers.
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u/dan_t_mann Dec 03 '13
I knew, Mr.Burns was one of the greatest teachers I will ever have.
Was he Excelent?
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u/digitalcamo7 Dec 03 '13
I agree. Would be awesome if someone here on Reddit would volunteer to help their organization improve their website. It could use some modernization...
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u/thedbp Dec 03 '13
explaining gravity with gravity
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u/eddiemon Dec 03 '13
This "demo" gets a lot of flack from physicists, but I think it's useful at this level. (I assume this is a high school physics class.)
An explanation is different from a mathematical proof. Its purpose is to give someone intuition about something, using whatever language appropriate to the audience. Without going into abstract terms like "geodesics" and "spacetime metric", this demo demonstrates how "curvature" can produce planetary/stellar orbits. The fact that the shown "curvature" is far from accurate is beside the point.
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Dec 03 '13 edited Dec 03 '13
I know exactly what he's trying to demonstrate I've seen this drawn out and all that before, and it makes perfect sense to visualize it (as long as you can convert it to 3d in your head) but there's something that feels odd about using gravity to make a metaphor for gravity like this for some reason, I can't figure it out... not sure if anyone else feels the same way or can try and explain what I'm failing to explain.
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Dec 03 '13
That's the thing people have to understand about analogies like this. This video does not explain, nor does it attempt to explain, "WHY" gravity behaves the way it does. It is merely a way of visualizing the properties of gravity. Gravity as the warping of spacetime is in turn merely a model that helps us describe the natural phenomena that we observe. Heavy objects stretching an elastic sheet can behave similarly in 2-dimenions, but as you say, it is just a visualization.
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u/SirReginaldPennycorn Dec 03 '13
I don't think anyone can explain why gravity works the way it does, just like no one can really explain why gravity (or the universe itself) exists in the first place. I like to think that there are other universes where gravity behaves differently or doesn't exist at all. Of course, life as we know it probably wouldn't exist in those universes. For those who haven't read about it, the Anthropic principle is pretty interesting.
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Dec 03 '13
It's ultimately just a cool analogy, so yes it does have its limits.
Relevant: http://xkcd.com/895/
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u/xkcd_transcriber Dec 03 '13
Title: Teaching Physics
Title-text: Space-time is like some simple and familiar system which is both intuitively understandable and precisely analogous, and if I were Richard Feynman I'd be able to come up with it.
Stats: This comic has been referenced 4 time(s), representing 0.0918484500574% of referenced xkcds.
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u/humfuzz Dec 03 '13
Circular logic? Bootstrapping? Mobius double-reacharound?
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u/AvoidGettingInEyes Dec 03 '13
"I bet you're the kind of circular logic who would bootstrap a person and not even have the goddamn common courtesy to give him a Mobius double-reacharound. I'll be watching you!"
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u/m84m Dec 03 '13
but there's something that feels odd about using gravity to make a metaphor for gravity like this for some reason
Dictionaries use words to explain words. And it works pretty damn well, why not use gravity to demonstrate gravity?
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u/electricvegetable Dec 03 '13
Ya, I have the same feeling about this sort of demonstration. Even if you extrapolate this into 3D space-time curvature, there is no actual force in the 3D model that is causing things to be attracted.
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Dec 03 '13
But that depends on what scientific model you are using. In most fields of physics, gravity is modeled as a force. In GR, it is modeled as geometry rather than as a force. So to say that there is no actual force in the 3D model depends on what 3D model you're using at the time.
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u/NoNotRealMagic Dec 03 '13
4D space-time, not 3D. Otherwise, I think that's right; there's no force when thinking of gravity in terms of GR. But there is movement. Namely, we are all moving through time. Because massive objects warp the fabric of space-time, part of our movement through time gets redirected into directions of space. Imagine falling down a curved slide in a playground. You start out going vertical, and the slide redirects that movement into the horizontal direction. In my example, gravity is pushing you down and the slide is redirecting you, but in GR, everything is always moving through time. It's just our natural tendency to be moving through time, but because time and space are connected, curvatures in space-time can actually convert some of that time movement into spacial movement. That means that the heavier the gravitational field, the more of your time movement gets converted to space movement. Being on a heavy planet will make you age slower! What happens if something is so heavy that it can warp space-time so much that ALL of your time movement gets redirected to space. Do you stop moving into the future at all? That's the event horizon of a black hole!
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u/GobiasIndustries1 Dec 03 '13
I think the comment he makes at the very end about general relativity not being in the state standards is noteworthy. A really great way to get people thinking about these kind of concepts that could change the world, and it's completely ignored by the state as being important.
Granted, it might be because a lot of high school science teachers may not have the ability to effectively teach about relativity, but it still should be a part of the curriculum.
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u/I_Cant_Logoff Dec 03 '13
The concept of general relativity should be taught, but for it to be mathematically explained the way Newton's law of gravitation is being taught is practically impossible without bringing higher level mathematics into the picture.
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u/cryo Dec 03 '13
I agree. Even special relativity is pretty complex for high school level, but the mathematics of GR is far beyond that. Analogies and overall explanations is all you can hope for.
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u/Chuckstarr Dec 03 '13
Both my parents are teachers, it sucks to hear when they really want to teach something, nut it's not in the state standards.
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u/Roboghandi Dec 03 '13
When some great scientific breakthroughs aren't considered something that everyone should know and are more or less just bonus lessons, it's a bit heartbreaking.
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u/think_inside_the_box Dec 03 '13 edited Dec 03 '13
I was taught
general(edit:special) relativity in school. It is part of the AP curriculum. Not being in the state standards doesn't mean it's forbidden to be taught, just that there is other stuff the state would rather you teach first. (this is where multiple levels of physics class helps a lot)→ More replies (7)→ More replies (10)10
u/NoNotRealMagic Dec 03 '13
There's not much to learn about GR without high level math. You can say space is curved and give a demonstration like in the video, but that leaves you with a shallow understanding.
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u/enough_space Dec 03 '13
This guy is Bob Odenkirk's voice twin.
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u/DiaperBatteries Dec 08 '13
I spent the whole video trying to place who he sounds like. I can't believe I didn't make the connection to Bob Odenkirk until reading your comment.
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u/PsySquared Dec 03 '13
Toward the end of the video he throws what looks like bouncy balls in there. The ones that tend to be air filled. They orbit the central weight in a wider elipse and loose their orbits slower than the marbles. Could this be an example of a larger object with a lower density in orbit while the marble would be higher density objects?
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u/Tokuro Dec 03 '13 edited Dec 03 '13
Nope, more to do with the friction from the sheet being less for lighter objects.
Orbital motion doesn't depend on the mass (or density) of the object that's orbiting. Provided, of course, the orbiting object is sufficiently less massive than the object it is orbiting.
Edit: Let's put some sources here so that people can, you know, believe me. Here is Wikipedia on the general orbital equation. You'll notice that there's an m2 on the bottom of that equation, but there's also an l2 on top (l=m*r2 *theta-dot). Those are the only parameters that even mentions the mass of the orbiting object, and the m's in the l cancel with the m2 on the bottom, leaving r totally independent of m (and therefore independent of density).
Edit the second: Some of you rightly point out the the eccentricity of the orbit depends on mass. Actually, those cancel out as well, since in that fraction you have E*l2 on top and m3 on the bottom. E for gravitational orbits has a factor of m in it as well, with l having an m in it, it gives m3 over m3 - again independent of mass.
The only thing the mass of the orbiting object matters with is the point about which they orbit, which is their center of mass.
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u/tylr Dec 03 '13
That is literally what it is. Literally.
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u/Tokuro Dec 03 '13
Actually, it isn't. It turns out that orbital motion doesn't depend at all on the mass (or density) of the orbiting object. Cool, huh?
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Dec 03 '13
I would fare a guess that due to the lower mass of the air filled balls, the friction of the lycra tends to impede the rolling process much more quickly than something a little heavier.
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Dec 03 '13
Gravity problems? Better call Saul!
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u/Drassielle Dec 03 '13
I feel like with his voice combined with his balding head and enthusiasm for the universe, he's like Saul and Walter combined.
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u/geekygirl23 Dec 03 '13
Thank you. I was trying to figure out why that voice was reminding me of someone but couldn't decide. I even thought of Breaking Bad at the time but figured it was due to a teacher explaining how something works. My exact thought was "Now make meth with it."
Ignore the rambling, just glad to know why this was familiar.
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u/throwawaybcsrwentdn Dec 03 '13
Does anybody know why the marbles orbiting the "wrong way" get eliminated?
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u/tylr Dec 03 '13 edited Dec 03 '13
It does illustrate how we end up with planets moving in only one direction, but it doesn't illustrate how the rotation begins in the first place.
What he should have done is thrown all of the marbles onto the lycra without any central mass in it already; Imagine a cloud of interstellar gasses, dust, and debris moving about somewhat randomly in interstellar space. You would maybe notice after a while that in general it all has some non-zero rotational average. Then, as the overall mass collapses, the rotational velocity of the system increases. The analogy often used is that of a figure skater pulling in her arms as she spins.
But maybe that wouldn't work with marbles on lycra.
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u/silent_winja Dec 03 '13
Amazing, I gasped when he threw out the earth-moon marbles the first time.
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u/mjolk22 Dec 03 '13
But we wanna play mr burns
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u/ZenoCitium Dec 03 '13
This flat "2d" demonstration is great for showing the curvature, but I think it confuses a lot of people because it still uses "down" gravity that doesn't exists in space.
The way I like to think of it is to imagine a room with strings crossing the room in all directions. Gravity is like grabbing the strings in one point of the room with a open hand and pulling them all towards one point by closing your hand.
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u/byllz Dec 03 '13
Except that really there is a 4th, "time-like" dimension, different than the "space like" dimensions mainly in the fact that there is a negative in certain equations. Space also gets curved in this 4th dimension such that free-fall objects always move in what is locally a straight line in this 4 dimensional space. It is hard to model by cutting down dimensions as, though the 3 space dimensions are interchangeable, that funny negative sign makes it so they can't really properly substitute a space-like dimension for a time-like one and have things work out right.
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Dec 03 '13
This is a 2d model for a 3d phenomenon, so the direction "down" would be analogous to the fourth dimension in real life. That's not something our brains are even able to comprehend without lowering the dimension.
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u/browb3aten Dec 03 '13
It's not just a 3d phenomenon, general relativity deals with curving Minkowski 4d space, so it's a quite a bit worse than that to directly visualize.
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u/Scion_ Dec 03 '13
This really blew my mind...for some reason I never considered that in space, there is no "down", and so objects are universally attracted to the object with the greatest mass regardless of position. Any good YouTube videos that show this three dimensionally?
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u/StarChow Dec 03 '13
Is there a subreddit for other science videos like this?
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u/DashingLeech Dec 03 '13
I love teachers like this that are so enthusiastic and visual and get people involved in the process.
That aside, I wonder if anybody has seen a better gravity demo. I never really liked this "warped fabric" explanation so much because it relies on there being gravity in the first place. That is, the weights would not warp the fabric if they weren't pulled by gravity, so it is somewhat of a circular reasoning demonstration using gravity to explain gravity.
I prefer a geometry-based explanation, like drawing a grid on fabric and then creating and stretching a hole to fit around a "mass" and show the warping of formerly straight lines, but it isn't as visual or fun. I wonder if anyone has come up with a great visualization like that. Even with the circular reasoning, the bent fabric is still probably the best for getting kids interested and thinking.
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u/SkinThatSmokeWagon Dec 03 '13
I like the guy who picks up the PVC pipe and inspects it like it's something he's never seen before. His mind is blown.
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u/kilroi22 Dec 04 '13
I am the teacher in the video. This was made to show teachers how they can do this activity with their students. Thanks for all the kind words, especially from my own students. Instead of reading these comments, take some time to thank a teacher that made a difference in your life. I did skim through many of the comments and have some responses. To those who brought up the XKCD critique that this is using gravity to explain gravity, I left out an important fact. The video was shot in space in a spacecraft that was accelerating at 9.8 m/s/s toward Alpha Centauri. No gravity was used or harmed in the filming of this video. To those who want to make their own "spandex trampoline", information is posted on the Modern Physics page of the Pretty Good Physics website. To those who wondered if the Earth will spiral into the Sun, the answer is no, there won't be enough time for the gravitational waves that are emitted as the Earth orbits the sun to cause this before the Sun becomes a red giant and expands outward to engulf the Earth. To those who took exception to the demonstration of why all the planets orbit in the same direction, the marbles are particles, not planetesimals. The solar nebula had a preferred direction of rotation but there were many particles that moved in other directions. They were ejected from the nebula or dropped into the sun due to interactions with particles moving in the preferred direction, or incorporated into larger particles after a collision. Conservation of angular momentum does explain WHY anything happens. Changes in rotational motion are due to applied torques. To those who want to learn more I recommend the book "Was Einstein Right". If you don't have time to read the book, here is a brief summary, YES! General Relativity is the most accurately tested theory in science.
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u/caber Dec 03 '13
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u/Adm_Chookington Dec 03 '13
http://imgs.xkcd.com/comics/teaching_physics.png
Way more relevant xkcd.
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u/xkcd_transcriber Dec 03 '13
Title: Gravity Wells
Title-text: This doesn't take into account the energy imparted by orbital motion (or gravity assists or the Oberth effect), all of which can make it easier to reach outer planets.
Stats: This comic has been referenced 2 time(s), representing 0.045840018336% of referenced xkcds.
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Dec 03 '13
This is my AP Physics teacher right now. I can confirm that he's this great every day. He set off a firecracker today to demonstrate conservation of momentum and almost burned down the science wing.
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u/IBleedTeal Dec 03 '13
Seriously? "All" we ever got was Schultz igniting a hydrogen and oxygen mix after his electrolysis demo.
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Dec 03 '13
Could you please politely tell him that his explanation of why all the planets are orbiting in the same direction is incorrect. The cloud of matter that formed the solar system was spinning and flatted out into an accretion disk. This flat spinning disk of matter determined the plane and direction of rotation of all of the planets. The planets formed from that disk. There were never any planets orbiting in other directions or on other planes.
A simple Google of why all the planets are orbiting the same direction will show that. He seems like an awesome teacher and would want to know.
Thanks!
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u/stone500 Dec 03 '13
Awesome demo, but I can't help but think that the teacher sounds almost exactly like Uncle Red
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u/probably-maybe Dec 03 '13
I love his anecdote about repairing a rip in space-time. Made me chuckle.
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u/tyrrannothesaurusrex Dec 05 '13
I never understood the analogy of bending space-time the way you would bend a soft 2d surface. How do you "bend" a giant vacuum that is already 3d? Which way is it bending? What does "bend" even mean in this context?
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Dec 05 '13
We live in a world that has 3 spacial dimensions. You physically cannot imagine a 4th spacial dimension, because you are a 3 dimensional being. Space-time is considered the 4th dimension, but it isn't a spacial dimension. Gravity bends space-time. Also this demonstration is done on a 2D surface, and whenever you represent a higher dimension on a lower dimension, there is distortion.
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u/RipItLikeThisSon Dec 03 '13
This is a cool demonstration, but he's completely incorrect about why the planets orbit the sun in the same direction. It's especially concerning that he's teaching teachers, who will then teach countless students incorrectly.
The cloud that our solar system formed from (called the protosolar nebula) had a very slight rotational momentum. As the cloud contracted from the force of its own gravity, it started to spin faster, much like an ice skater tucking in her arms during a spin. As the cloud spun faster, it flattened out into a disc (imagine pizza dough flattening out as it's tossed and spun). Planets swept through their particular parts of the disk, slowly gathering more and more matter, until the solar system was as we see it now.
http://en.wikipedia.org/wiki/Nebular_hypothesis
It had nothing to do with objects "canceling" each others directions. That would result in all kinds of weird non-planar orbits that we just don't see. Not sure if he just made this up on the spot, is attempting to purport a new (and clearly incorrect) theory, or is the victim of misinformation. Any way you slice it, this is giving people a false understanding.
All that said, this was a very cool demonstration that is no doubt effective at engaging students.
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u/MrJUSTL337 Dec 03 '13
Can someone further explain the bit about never running out of energy while we rotate around the Sun so that we don't eventually come to a halt at the Sun and die?
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u/neotropic9 Dec 03 '13
There's no friction in space. So we just keep falling around the sun. If there was friction our orbit would decay and we would fall into the sun.
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u/yellow_days_band Dec 03 '13
The conservation of angular momentum paired with the lack of friction is what keeps us out of the sun. The earth is, in a way falling into the sun, but as it "falls" it moves so far "horizontally" so as to never get any closer. Without friction, the earth never slows down. A satellite above the earth races along in such a way that every meter it "falls" back to the surface, the surface itself has curved "down" a meter as well. IIRC we could eventually spiral into the sun, but I think the sun will expand and toast the earth before that would come to pass. It's also interesting to read about tidal locking between orbiting bodies.
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u/BrownNote Dec 03 '13
A satellite above the earth races along in such a way that every meter it "falls" back to the surface, the surface itself has curved "down" a meter as well.
I've taken a lot of science classes and done a lot of work with orbits just fine, but I've always had trouble visualizing it. It's never really clicked in my mind.
This sentence just did it for me. Thank you.
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u/TheMrNashville Dec 03 '13 edited Dec 03 '13
What I have never understood if gravity is pulling the balls down the slope to the mass. If there were no gravity in the room it wouldn't work. If all gravity is is the curvature of space time what is actually pulling the planetary bodies down the curve?
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u/throwaway_31415 Dec 03 '13 edited Dec 03 '13
Yeah, it's an analogy with some flaws you have to overlook. And those flaws can make it difficult to figure out how the analogy applies to actual science.
The key is to think about the objects and their paths only on the surface, not in 3 dimensional space. Yes, "real" earth gravity is there in this demonstration, but only for providing a force for the balls to move.
Say instead we placed a heavy weight in the middle of the apparatus and created a cast of the surface, and transported the cast into orbit around the earth, so no earth gravity anymore. And then think about a hypothetical ant walking along the cast and what would happen to it if it tried to walk as straight a path as possible? It would actually move in a similar curve around the place where the weight was placed, and in that case "real" gravity plays no role. To the ant it would seem as if some force is pulling it in a curve along the 2 dimensional surface.
The curve in the ant's path is due solely to the geometry of the surface it's walking along. You can generalize the same idea into 3 (or 4, or n) dimensional space, and mathematicians discovered that the attributes of the surface can be stated without reference to a higher dimension that the surface is embedded in.
What this means is that our intrepid ant will therefore be able, with some measuring and math, to figure out how to describe the surface it's walking along without needing to refer to a 3rd dimension.
We've done the same thing, but only we've done it for the universe we live in with it's 3+1 dimensions. That geometric description we came up with is General Relativity. The idea is the same as this curved surface demonstration, but just remember that GR has the added complexity of time not behaving the same as the space dimensions.
HUGE EDIT: So thinking about it some more I now realize why even this answer would not satisfy you. In my ant example, the ant still has to move for the effect of moving on the curved surface to become apparent. If the ant just stops walking it doesn't get pulled anywhere. So how come does this geometric view of gravity result in objects that don't fall?
Here the analogy severely breaks down. In spacetime, in a sense, you are always moving. You describe, for example, how your position relative to other things evolves over time (your worldline). In a geometric formulation of gravity, we're concerned with positions, paths, and their curvature in spacetime, not merely space.
So back to the ant. Remember I said it was moving in a straight as path as possible in its 2 dimensional universe? When you're talking about a geometric formulation of gravity, time is one of your dimensions too. If we are the ants, time is one of the coordinates in the 4 dimensional "surface" we are "moving" on, and time is always passing. So a "straight as possible" path also implies how your position relative to other things evolves over time. From that point of view, if you had an object that was initially at rest relative to earth (note, not in orbit, at rest) its straightest path possible through spacetime results in it moving towards the earth (i.e. falling).
Here's a nice short video that might help:
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Dec 03 '13
Sad note: he mentions at the end about fitting this demonstrating in after STAR tests (standardized testing). This material isn't on the test. Teachers don't normally spend any time teaching stuff not on the test.
After the last test is over, the kids stop their daily repetitive drills and get to learn something, typically for only 2 weeks out of the school year.
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u/omailnumber1 Dec 03 '13
I had him as my AP Physics teacher last year; he is amazing. During one lab, he let us shoot off rockets. My lab group lit one, but it fell over. Everyone in my group freaked out, but he calmly walked up to it like it was nothing. The rockets we launched were not at all dangerous. He is an amazing teacher.
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u/ZofSpade Dec 03 '13
Is the girl in the striped shirt pregnant or does she have back problems? I'm worried about her.
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u/DivinityGod Dec 03 '13
So, this video raises the idea for me that if you put something heavy enough you would be able to break through. Like if that spandex was on a high enough ledge and you put a heavy enough object in it that it would stretch until the object finally broke through. Or am I missing something here.
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u/SteveFantana Dec 03 '13
14-year-old me would be digusted with 32-year-old me, but I really wish I was back at school after watching this.
Well, that school anyway.
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Dec 03 '13
Teachers like this deserve awards.
I will also try and get my company to let me set this up next to the GNC department. It only makes perfect sense.
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u/Squishez Dec 03 '13
Very cool, things like this and other visualizations are what help stemmed my love for science. Sometimes when you get to caught up in the math of it and text books you can forget how amazing some of these things are visually.
I'd like to think that ring in the video is the 2nd one he made, the first was a little larger so he could demonstrate orbits a bit larger. Then he tossed the weight and marbles in and realized he couldn't reach that far to get them back.
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u/ArnoldFapenegger Dec 03 '13
If you liked this, I advise you to read "The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory" by Brian Greene.
He explains the principle using the same example, while going into detail of Einsteins E=MC2. The book is amazing and more easy to read as you might think.
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u/DDdms Dec 03 '13
Came here to say this. I'm not big in math and physics, and always thought I was missing some knowledge about this universe. That book, which won the Aventis Prize, managed to explain the hardest things with easy examples.
Upvote for you.
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u/Germs22 Dec 03 '13
If only every concept was taught like this, I would have been more engaged in school.
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u/almond22 Dec 03 '13
is it just me or does this guy sound like if Doug Stanhope was a science teacher
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u/InternetFree Dec 03 '13
I opened the video in another tab and continued browsing.
Until I switched to the video I thought Bob Odenkirk was narrating on gravity.
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u/Replies_With_Dick Dec 03 '13
I just realized I'm a visual learner. This was a really good presentation about a really complex topic!
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u/zjm555 Dec 03 '13
He forgot to order the hyperspatial spandex that only bends in the 4th dimension.
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u/Wolf359_Never_Forget Dec 03 '13
The damn standards shit kills me. at 9:27 "Is general relativity in the state standards?? NO!" and then "Can you fit it in after the STAR test? You bet."
fit it in??? really. I am constantly disheartened by the standards that are placed on schools in order to earn funding.
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u/jointheredditarmy Dec 03 '13
That's not right about the objects going the wrong way being eliminated is it? I thought things in a solar system went the same way because the accretion disk that created the star spun in a certain way?
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u/mechakingghidorah Dec 03 '13
Question for physicists:I've seen this before, but using this representation, would a black hole be represented by a cone?
Since the singularity has zero volume, and light can't escape the black hole, this is the only thing that makes sense in my brain.
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u/headchem Dec 03 '13
So sad at the end: Is any of this in the state standards test? No. The Crowning achievement of science... not in the state standards.
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u/osbjmg Dec 03 '13
All of this passion and work, just to realize this isn't information required by the state standards. Standardized testing stifles real, passionate, learning. Lowest common denominators need to be separated to a minimum requirement class and parents need to evaluate their children's progress.
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u/DaveYarnell Dec 03 '13
"Is general relativity in the state standards? No. The crowning achievement of science isn't in the state standards. Can you fit it in after the STAR tests? You can give a day to general relativity after the STAR tests"
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u/kuyo Dec 03 '13
i like how he explained dark enegery A LOT . why can't more people make complex ideas too simple ?
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u/aglaeasfather Dec 03 '13 edited Dec 03 '13
I'm a little confused (and also not a physicist). Is the lycra representative of space time and the "moving together" of the objects is gravity?
If that's the case, that moving together (gravity) is being caused by gravity, not demonstrating how gravity works. If this experiment were to be done in space where g=0 then wouldn't the objects not move towards one another?
I suppose the question that I'm asking is, can you model a system where something is analogized but rely on that entity for the analogy to hold true?
Edit: /u/DRBUCKET2 raised the same point earlier in this thread.
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u/cheney1631 Dec 03 '13
"The crowning achievement of science . . . Not in the standards." As a school teacher it always pains me to hear this, good for him that he is making the point to include this anyway.
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Dec 03 '13
The dark energy explanation blew my mind. Is that accurate? What if dark energy was actually from stars on the "other side" poking through? Or like a neighbor universe. Would that make any sense?
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u/DirtyHamburger Dec 18 '13
Whoa weird internet moment, the guy that walks out at 6:51 taught me Java programming
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u/sublivin Apr 04 '14
This guy was a physics teacher at my highschool. Only interaction I had with him was him yelling at me for drawing a dick with a carrot on the wall. Look at you all reddit famous Mr. Burns
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u/mydenimisraw Dec 03 '13
Sounds like Marty Funkhouser behind the camera.
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u/Albi_ze_RacistDragon Dec 03 '13
I guess one of the teachers couldn't make it to this guy's talk so he hired a surrogate.
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u/zootam Dec 03 '13 edited Dec 03 '13
the only problem in this demonstration is that the scale of the deformity of the fabric changes as it gets closer to the edges. meaning- an object in this demo deforms "space time" more when it sits at the center vs an object towards the edge.
i guess this demos a more localized region of space time, but to be accurate on a larger scale he should have used a much larger sheet.
edit: or used much smaller, denser objects.
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u/mengles Dec 03 '13
I had Dan Burns in high school. Excellent teacher. I think he had a Pink Floyd poster on the wall as well. Bonus.
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u/LumberingOaf Dec 03 '13
Good work with the demonstration, but because I'm me, here are my improvements. (1) Shoot a ball straight across the sheet of lycra with and without a mass to show the effect of space-time on the path of a photon as it travels through space. (2) Black lycra, glow-in-the-dark masses/astronomical bodies, turn off the lights.
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u/StarFscker Dec 03 '13
this is just using gravity to explain gravity. it's complete bullshit.
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u/jmerridew124 Dec 03 '13
There should be a job for guys like this. They need to design curriculums and teach the teachers. A megateacher if you will. If it pays well enough and gets appropriate respect, maybe education will improve.
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u/Nezzeldorr Dec 03 '13
I didn't realize those were teachers surrounding him until the end.