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  2. Napkin ring problem - Wikipedia

    en.wikipedia.org/wiki/Napkin_ring_problem

    Lines, L. (1965), Solid geometry: With Chapters on Space-lattices, Sphere-packs and Crystals, Dover. Reprint of 1935 edition. A problem on page 101 describes the shape formed by a sphere with a cylinder removed as a "napkin ring" and asks for a proof that the volume is the same as that of a sphere with diameter equal to the length of the hole.

  3. Hole argument - Wikipedia

    en.wikipedia.org/wiki/Hole_argument

    This means that one source, the Sun, can be the source of many seemingly different metrics. The resolution is immediate: any two fields which only differ by such a "hole" transformation are physically equivalent, just as two different vector potentials which differ by a gauge transformation are physically equivalent. Then all these ...

  4. Umbra, penumbra and antumbra - Wikipedia

    en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra

    Umbra, penumbra and antumbra of Earth and images that could be seen at some points in these areas (Note: the relative size and distance of the bodies shown are not to scale.)“… The Earth’s shadow has two distinct parts,… the UMBRA is the part of the shadow where all direct sunlight is blocked by the Earth; the PENUMBRA of the shadow is ...

  5. Boring (earth) - Wikipedia

    en.wikipedia.org/wiki/Boring_(earth)

    Boring is drilling a hole, tunnel, or well in the Earth. It is used for various applications in geology, agriculture, hydrology, civil engineering, and mineral exploration. Today, most Earth drilling serves one of the following purposes: return samples of the soil and/or rock through which the drill passes; access rocks from which material can ...

  6. How long it really takes to fall through the Earth - AOL

    www.aol.com/news/long-really-takes-fall-earth...

    The original calculations assumed that the Earth has the same density throughout - and the gravitational force changes as you approach the center, much like the weight of a spring that bounces up ...

  7. Earth's magnetic field - Wikipedia

    en.wikipedia.org/wiki/Earth's_magnetic_field

    The rotation axis of Earth is centered and vertical. The dense clusters of lines are within Earth's core. [2] Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun.

  8. NASA image of Earth reignites North Pole is hollow conspiracy

    www.aol.com/news/2016-05-23-nasa-image-of-earth...

    Now conspiracy theorists say NASA is hiding the fact that Earth is really hollow and that inside is another world, where aliens and animals that look like woolly mammoths live.

  9. Schiehallion experiment - Wikipedia

    en.wikipedia.org/wiki/Schiehallion_experiment

    The Earth has a mass M E, radius r E and a density ρ E. The two gravitational forces on the plumb-bob are given by Newton's law of gravitation: =, = where G is the Newtonian constant of gravitation. G and m can be eliminated by taking the ratio of F to W: