Awesome Physics Teacher Dan Burns Explains Gravity In A Way Anyone Can Understand

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General relativity, the geometric theory of gravity developed by Albert Einstein in the early 1900's, is today considered one of the twin pillars of modern physics. Along with quantum mechanics, it is fundamental to our understanding of the universe.

Yet despite its importance, general relativity doesn't always get the classroom attention it deserves.

"Is general relativity in the state standards? No. Probably the crowning achievement of science not in the state standards," Dan Burns, a physics teacher at Los Gatos High School in California, says in the video above. But that didn't stop Burns from coming up with an ingenious demonstration to help students understand concepts that are notoriously tricky.

Written By: Cate Matthews
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36 COMMENTS

    • In reply to #3 by prettygoodformonkeys:

      “Both objects warp space-time, and they FEEL that, so they come together.”
      Sorry, but: WTF kind of explanation is that?

      I think it is a simple figure of speech. – Like two magnets “feeling” (or if you prefer “responding to”) the force of attraction.

      obzen -@ 4 -one problem. friction :)

      Yes that does spoil it a bit. The sagging does show the gravity wells in proportion to the mass of the objects and coming together of large attracted objects, but the friction spoils the orbital demonstrations a bit.
      If there had been a second area with a similar profile made of a hard low-friction material, (like the coin boxes used by charities) the small balls would have demonstrated trajectory deflections and orbits much better.

      There is a lot of detail and some good images on this link.
      INTRODUCTION TO GRAVITY-WELL MODELS OF CELESTIAL OBJECTS

    • In reply to #3 by prettygoodformonkeys:

      “Both objects warp space-time, and they FEEL that, so they come together.”
      Sorry, but: WTF kind of explanation is that?

      First off, I have to say I do not understand relativity, but in what why would the demo be different if only Newtonian gravity applies? & if there is no difference, what kind of explanation is that? (I Just want to know.)

      &- In reply to #20 by mikfromoz:

      silly question. in reality how far apart can objects be and still gravitationally influence each other?

      Actually I think that is a great question.

      • In reply to #26 by old-toy-boy:

        >

        First off, I have to say I do not understand relativity, but in what why would the demo be different if only Newtonian gravity applies? & if there is no difference, what kind of explanation is that? (I Just want to know.)

        The demo model is simplistic and not accurate in detail, so the differences between Newtonian gravity and Relativistic gravity cannot possibly be illustrated by this demo.

        The point of the demo is to convey the relativistic concept that the presence of mass distorts space and that it is the curvature of space that influences the way things move through it. The model uses the distortion of the lycra to represent the curvature of space.

        The Newtonian theory of gravity is simply a mathematical description and makes no attempt to explain the actual mechanism of how the gravitational force takes effect. So a purely Newtonian demo would be difficult to construct. You are pretty much left with the classic orrery, which is much less fun.

      • In reply to #26 by old-toy-boy:

        In reply to #20 by mikfromoz:

        silly question. in reality how far apart can objects be and still gravitationally influence each other?

        Actually I think that is a great question.

        The force of gravity diminishes with the inverse square of the distance, so it theoretically has influence all the way to infinity, but will be approaching an infinitely small force out there.

        Our Sun’s gravity, is too weak to retain orbiting planets about 2 light-years out, But the gravity of the Milkyway and Andromeda galaxies (at 2.5 million light-years) is strong enough to bring them together to collide and possibly merge in about 3 to 5 billion years time.

        There is a nice animation here:-

        Video- File:Andromeda and Milky Way collision.ogg

    • In reply to #7 by crookedshoes:

      BTW, does this suggest that there is a “down” and “up” to the universe? Or is it such an over simplification that it only seems like that?

      That question reflects the inherent deficiency in this demonstration. What really is being shown is the effect that mass is having on the 2-dimensional universe that is the fabric. For both objects there is no up or down, and what we see as a displacement in the z-axis the objects “see” as a pull between the objects that varies due to proximity. It really is a brilliant conceptualization for the effect of gravity on spacetime.

      • So, if were to try to REALLY model this, the warping of space time would be in 3 dimensions (or 4)? I have always seen it in this type of model. I also have seen documentaries where they show that space time is curved. I saw a scientist draw a huge triangle on the sand of some beach somewhere. She then measured the angles and demonstrated that they did NOT add up to 180.

        She used this to show that earth was curved. She then did the same thing with stars and demonstrated the curvature of space. I get it but don’t get it.

        In reply to #9 by elmo14:

        In reply to #7 by crookedshoes:

        BTW, does this suggest that there is a “down” and “up” to the universe? Or is it such an over simplification that it only seems like that?

        That question reflects the inherent deficiency in this demonstration. What really is being shown is the effect that mass is hav…

        • Don’t beat yourself up if you cannot visualise in your mind’s eye the curvature of 3D space. I don’t think anybody can, probably not even Albert Einstein himself could! You would have first have to be able to visualise things in 4D. That’s a huge ask because our brains have evolved to make sense of a 3D world. Even the best mathematicians and scientists have to make do with an understanding of the geometric equations.

          It might help to understand the concept by visualising flat and curved space in fewer dimensions.
          A ‘flat’ 1D space can be represented by a straight line drawn on a piece of paper. A curved 1D space can be represented by a curved line on a flat piece of paper. A curved 1D space can also be curved into a 3D space: imagine forming a wire into a coiled spring shape for example.
          A flat 2D space can be represented by a flat sheet of paper. We can visualise such a 2D space being curved by curving the sheet of paper into a cylinder. Alternatively think of the curved 2D surface of a globe, as per your huge triangle example on a beach. Both these examples can be visualised very easily from the vantage point of our 3D world.
          But what I cannot imagine is how a 2D curved space looks when curved into a 4D space.
          Nor can I imagine what a 3D space looks like when curved into a 4D space and there is absolutely no chance of conceiving what a 3D space curved into 5D might be like!

          All of that said, the lycra model shown here actually works very well because almost everything in our solar system is orbiting the sun in the same 2D plane.

          In reply to #11 by crookedshoes:

          So, if were to try to REALLY model this, the warping of space time would be in 3 dimensions (or 4)? I have always seen it in this type of model. I also have seen documentaries where they show that space time is curved. I saw a scientist draw a huge triangle on the sand of some beach somewhere. S…

  1. I noticed he slipped a minor ‘god” comment in there, probably to placate any religious students for no necessary reason.

    On the other hand, I liked the demo about everything starting in different directions, but resulting in a few moving in the “preferred” direction.

  2. It’s a shame that kids are allowed to be fooled so much by scientists, the religious mob, and Dawkins himself. When will all of this religious behaviour stop? Science is a religion.

    • In reply to #10 by Pincho Paxton:

      It’s a shame that kids are allowed to be fooled so much by scientists, the religious mob, and Dawkins himself. When will all of this religious behaviour stop? Science is a religion.

      Sarcasm/humour?? Can’t see any value in this.

      • Pincho is a new profile. Clearly a drive by, best to treat with the contempt it deserves

        In reply to #12 by Fritz:

        In reply to #10 by Pincho Paxton:

        It’s a shame that kids are allowed to be fooled so much by scientists, the religious mob, and Dawkins himself. When will all of this religious behaviour stop? Science is a religion.

        Sarcasm/humour?? Can’t see any value in this.

      • In reply to #12 by Fritz:

        In reply to #10 by Pincho Paxton:

        It’s a shame that kids are allowed to be fooled so much by scientists, the religious mob, and Dawkins himself. When will all of this religious behaviour stop? Science is a religion.

        Sarcasm/humour?? Can’t see any value in this.

    • In reply to #10 by Pincho Paxton:

      It’s a shame that kids are allowed to be fooled so much by scientists, the religious mob, and Dawkins himself. When will all of this religious behaviour stop? Science is a religion.

      What….I don’t even….

  3. It just annoys me that people still use this bending of space time when all you have to do is pull a plug out of a sink with a paper boat in it. Then the water bends, but then it is a flow force into a hole, and the boat moves towards the hole. So you get the bend, and you get the flow, but it isn’t the bending of water that moves the boat, its the flow. Look…

    http://www.ultimategenius.webspace.virginmedia.com/ZeroGravityPictures.jpg

    • In reply to #18 by Pincho Paxton:

      It just annoys me that people still use this bending of space time when all you have to do is pull a plug out of a sink with a paper boat in it.

      Perhaps you should learn some science instead of being annoyed by simple explanations of facts. My links @16 show how objects are drawn towards or into the gravity wells of galaxies, stars, planets, moons etc. along curved trajectories.

      So you get the bend, and you get the flow, but it isn’t the bending of water that moves the boat, its the flow. Look…

      Nope! It’s the gravity pulling the water and the boat down the hole together, with the Coriolis effect causing the rotation, with the boat going down the curved slope of the water. – Just like the trainee astronaut occupants of the “Vomit Comet” float apparently weightless and falling freely at the same speed as the aircraft!

        • In reply to #22 by FreeWillyB:

          In reply to #21 by Alan4discussion:

          You may be overestimating the role of the Coriolus effect:

          You are correct. – It is dependent on the diameter of the rotating fluid, and the difference in the speed of the rotating Earth at different latitudes across that distance, so yes it can be easily overpowered by other local forces in that analogy – especially on a small scale such as irregularities in the bath outlet pipe -. However on the larger scale such as hurricanes on Earth, or on the astronomical scale we were discussing, it is very much a force to be noted.

    • In reply to #19 by Net:

      i still don’t understand where the masses get the energy to move in their attraction to one another

      Potential energy. Two masses m1 and m2 at a distance r have a gravitational potential energy of – G m1 m2 / r.
      See this

    • In reply to #20 by mikfrmoz:

      silly question. in reality how far apart can objects be and still gravitationally influence each other?

      Not silly. Two objects, each with mass, gravitationally influence each other over any distance. But the gravitational force of attraction reduces in proportion to the square of the distance between them. So, in practical terms, the influence of gravity at very large distances becomes negligible.
      The force of attraction is also proportional to the mass of each object. So very massive objects, such as a massive star, or a black hole, have a noticeable effect on objects at greater distances than a single planet.
      And galaxies, typically consisting of billions of stars + dark matter, exert gravitational pull on each other over truly vast distances.

  4. Come on you preachers forget all the Jesus and Allah bollocks!
    Teach your congregation science.
    You will of course need to be educated in the meaning of empiricism ;as opposed to the baloney that is infecting your mind!

  5. Nice demo, but not new. Have seen this used many times. First time, I think, was in an Open University programme going back quite some years. Seen it used recently on The Sky at Night on BBC television.

  6. This video DOES NOT explain Gravity. Why? Because it speaks about deformation of the Space-Time
    produced by the object that you put in the center . But The fact is that that object deforms the cloth because
    there is the EARTH’S Gravity below the cloth. And the little balls roll down BECAUSE of EARTH’S gravity
    and not because the mass in the center of the cloth. So you don´t explain Gravity with this video.

  7. Pincho is a new profile. Clearly a drive by, best to treat with the contempt it deserves

    In reply to #12 by Fritz:

    In reply to #10 by Pincho Paxton:

    It’s a shame that kids are allowed to be fooled so much by scientists, the religious mob, and Dawkins himself. When will all of this religious behaviour stop? Science is a religion.

    Sarcasm/humour?? Can’t see any value in this.

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