Recently, I finished gravitation. I wonder why the shapes of planets or any body revolving around any star are not cubical or ellipsoidal. In our solar system all the planets are spherical in shape. Why isn't a body of any other shape found revolving around the gravitational field of any star?
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Isn't it due to the fact that spherical bodies have low surface tension – Utkarsh futous Apr 01 '17 at 16:26
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1Possible duplicate of Is it possible to prove that planets should be approximately spherical using the calculus of variations? – M. Enns Apr 01 '17 at 16:26
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Actually i am just asking a valid reason why we dont observe or see a cubical or body of any other shape revolving around a star in space – Prajwal Apr 01 '17 at 16:34
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https://spaceplace.nasa.gov/planets-round/en/ – Apr 01 '17 at 16:57
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Because it isn't the configuration that minimises their total energy. – ProfRob Apr 01 '17 at 17:12
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A sphere is the shape that minimizes gravitational potential energy. For a perfect sphere of uniform density there would be no gain of energy from moving the location of any body. Of course, on Earth there is plate tectonics that pushes up mountain chains, but gravity together with weather wears them down again so that Earth is an approximate sphere if we discount the equatorial bulge due to its rotation. – Lewis Miller Apr 01 '17 at 17:13
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Another possible duplicate: http://physics.stackexchange.com/q/26297/2451 – Qmechanic Apr 01 '17 at 17:15
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All massive bodies are ~spherical in shape due to their own gravity, not because they orbit around a star or a galaxy center.Gravity works inwards from all directions, towards center of mass, causing the bodies to become spherical. These bodies are not only planets, but also stars themselves.
There can be smaller (less massive) bodies that can be in different shapes because they have less gravity and their material can withstand their gravity in that shape. Massive bodies have higher gravity and the only stable shape in that case is spherical.
kpv
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Every material would have some shearing stress limit (there are no true rigid bodies). Considering this, if sufficient material accumulates together in a small region, it would cause the material to collapse into a spherical shape due to its own gravitational force (the shape of lowest potential energy).
Accordingly, if the material were extremely hard or less in quantity (e.g. asteroids), the body may not be spherical.
pulsejet
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