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Raisin-toe
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Really what is gravity, I don't understand.
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A common but very misleading analogy. It omits the time dimension of space-time, which is crucial to explain gravity. Imagine the marble initially at rest. Explain why it starts moving towards the bigger mass on the rubber sheet. But without using gravity to explain gravity!DaveC426913 said:The usual 2D analogy is that of a bowling ball and a marble resting on a rubber sheet.
A.T. said:Imagine the marble initially at rest. Explain why it starts moving towards the bigger mass on the rubber sheet. But without using gravity to explain gravity!
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This is not the marble-rolling-on-a-rubber-sheet-analogy I criticized. But I doubt it is much better. A layman will ask: If the space accelerates in all directions, how come the radius of the Earth stays constant.yogi said:Easy - have 4 persons each grab one corner of the rubber sheet in free space and accelerate all 4 corners in the same direction - the fabric will be indented by the F = ma reactance of the mass to the acceleration
Actually, the FIRST thing a layman will say is: "rubber sheet? Ohhhhhhh! That makes more sense than what I had on my head up till now..."A layman will ask: If the space accelerates in all directions, how come the radius of the Earth stays constant.
DaveC426913 said:I hear people complain about the rubber sheet analogy being flawed all the time.
It's almost a hundred pages! We were looking for something "in a nutshell".A.T. said:In fact, I have no problem with the rubber sheet, but with the marbles rolling into dimples created by bowling balls.
The rubber sheet with a big dimple can be used as an analogy for curved space. But curved space does not make apples fall from trees.
Thats why it is misleading.A.T. said:It doesn't? Why not? An apple will roll down the rubber hill.
It confuses those really interested in the topic. They stop thinking about it, assuming that they are not smart enough to grasp it. But in fact it's very easy and can be explained in a way that is both: correct and visual. http://fy.chalmers.se/~rico/Theses/tesx.pdf"
A.T. said:But curved space does not make apples fall from trees.
Curvature of space affects only objects, which are already moving trough space. The apple is initially at rest in space, and therefore not affected by curved space at all. You need curved space-time to explain why it starts moving trough space. But space-time is not a rubber sheet with a dimple.DaveC426913 said:It doesn't? Why not?
Why should it roll down? Because of gravity? This is explaining gravity with gravity.DaveC426913 said:An apple will roll down the rubber hill.
A.T. said:But in fact it's very easy and can be explained in a way that is both: correct and visual. http://fy.chalmers.se/~rico/Theses/tesx.pdf"
Then just take Figure 2.9 and some explanation. Chapter 2 is everything "in a nutshell" (8 pages, mostly pictures).DaveC426913 said:It's almost a hundred pages! We were looking for something "in a nutshell".
I've read this and read this and I can't make heads or tails of any of the sentences in it.A.T. said:Curvature of space affects only objects, which are already moving trough space. The apple is initially at rest in space, and therefore not affected by curved space at all. You need curved space-time to explain why it starts moving trough space. But space-time is not a rubber sheet with a dimple.
Phew. I understand spacetime and gravity pretty well, but I'm gonig to need to concentrate to read through the whole paper to understand what they're getting at. You can't simply read one section (eg.: what's a "staff"?)A.T. said:Then just take Figure 2.9 and some explanation. Chapter 2 is everything "in a nutshell" (8 pages, mostly pictures).
Your questions suggest that you are not differentiating between "curved space" and "curved space-time".DaveC426913 said:I've read this and read this and I can't make heads or tails of any of the sentences in it.
A.T. said:"The apple is initially at rest in space, and therefore not affected by curved space at all."
Isn't this obvious? Intrinsic curvature of a manifold merely implies certain distances between coordinates. But distances are pretty irrelevant, if you are not moving on the manifold.DaveC426913 said:What? Why not?
But not longer than 30min. I believe that laymen asking questions about gravity in this forum a those who really want to understand the topic. They often already know the marbles-on-a-rubber-sheet-analogy and cannot make sense of it (for good reason).DaveC426913 said:No, it is a beginner's lesson, it just takes longer than 30 seconds to get.
Gravity is a force that exists between two objects with mass. It causes objects to attract each other towards their center of mass.
Gravity works by the principle of mass attracting mass. The more massive an object is, the stronger its gravitational pull. It also depends on the distance between two objects - the closer they are, the stronger the gravitational force.
Sir Isaac Newton is credited with discovering gravity in the 17th century. His famous law of universal gravitation explains the relationship between mass, distance, and gravitational force.
Gravity is a force that exists between two objects, while weight is a measure of the force of gravity on an object. Weight can vary depending on the strength of gravity, but mass remains constant.
Understanding gravity is crucial for many scientific fields such as astronomy, physics, and engineering. It allows us to predict and explain the motion of objects in space, design structures that can withstand gravitational forces, and study the behavior of celestial bodies in our universe.