Imagine a man-made object, let's say a dumbell, that was so long it wrapped around the Equator. Never mind the extreme difficulty of manufacturing such an object, let's assume it could be done. Let's also pretend that there is someone who could actually lift that much weight. If she tried, what would happen? By the way, this hypothetical person is so strong that she can continue to lift the dumbell even once the other end hits the Earth's core.

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    $\begingroup$ Given all your hypotheticals, the dumbbell would not be lifted. Her feet would sink into the Earth instead. $\endgroup$
    – James
    Oct 14 '19 at 13:34
  • $\begingroup$ What does "lift" mean when you are talking about an object that completely encircles the Earth? Are you talking about a rigid motion? In that case, moving one side of it further from the center of the Earth would mean moving the opposite side closer to the center of the Earth. Are you talking about stretching the object so that every part of it could simultaneously be moved further from the center? In that case, it's hard to imagine how a single person standing in just one spot could achieve it. $\endgroup$ Oct 14 '19 at 13:52
  • $\begingroup$ Hi K Man. This question is better than the version you posted on Astronomy, but it still has room for improvement. Why does one end of the dumbbell hit the Earth's core? Why posit an impossibly strong person to lift it, rather than a machine of some sort? Such a machine could have a broad base, so that the pressure on the ground isn't focused onto a tiny area. $\endgroup$
    – PM 2Ring
    Oct 14 '19 at 14:21
  • $\begingroup$ @Solomon Slow I mean that as you lift the object "up" on one side of the planet, it is going "down" on the other side. $\endgroup$
    – K Man
    Oct 14 '19 at 15:59

Your dumbbell bar would be very floppy.

Consider a steel guitar string, which is quite floppy, even though it's made of steel. Now scale up the size of the string by 10 times (in all 3 dimensions). Its cross-section is now 100 times bigger, so it's 100 times stronger, but its mass is 1000 times bigger, so the extra strength isn't enough, and the string is therefore 10 times floppier. This is called the square-cube law.

Your giant dumbbell is a lot bigger than that, so it will be extremely floppy, and it will irreversibly stretch itself from its own weight in even a very weak gravitational field.

The square-cube law is a very useful piece of mathematics in physics and engineering. Here's a brief excerpt from Wikipedia:

The square–cube law (or cube–square law) is a mathematical principle, applied in a variety of scientific fields, which describes the relationship between the volume and the surface area as a shape's size increases or decreases. It was first described in 1638 by Galileo Galilei in his Two New Sciences as the "...ratio of two volumes is greater than the ratio of their surfaces".

This principle states that, as a shape grows in size, its volume grows faster than its surface area. When applied to the real world this principle has many implications which are important in fields ranging from mechanical engineering to biomechanics. It helps explain phenomena including why large mammals like elephants have a harder time cooling themselves than small ones like mice, and why building taller and taller skyscrapers is increasingly difficult.


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