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B.O.B DOLE
Why are bubbles round and why are planets round?
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More correctly, round should be replaced by spherical, but in practice they are not always. Some big bubbles wobble about in rather strange shapes. Look at John Prescott for example. The Earth is not quite "round" it bulges a bit round the equator.
B.O.B DOLE said:
Bubbles are truly spherical only in a vacuum, but the broadly spherical shape is the result of a molecular force commonly as surface tension.
I'm not so clued up about planets, but a reasonable postulate would be that the shape is formed while the planet is still very hot and generally very molten, and that gravitational force therefore is a big factor in determining the shape.
They're round cos square bubbles would look weird. 
Picking up an old fluids textbook, I think I have the answer: Laplace's law states that by increasing the radius of a fluid vessel, the wall tension necessary to keep the system in equilibrium also increases. Now, a sphere is the shape where you have least distance from the centre to the outermost point, i.e. that with the smallest vessel radius.
We also know that the gas pressure throughout the bubble is uniform (Pascal's law).
So, if the bubble deviates from the spherical shape, the bits that are further away from the centre of the bubble than for a spherical bubble will get pushed in (because the gas pressure is not sufficient to cancel out the wall tension), and the bits that are nearer from the centre will get pushed out.
Hence, the bubble finds equilibrium in a spherical shape.
The planetary one is indeed down to gravity. This one is far easier. As you know, everything tries to get to a lower state of gravitational potential energy. If you hold something in the air and let go, it falls to the earth. So, the sphere is the shape of least gravitational potential energy. Of course the Earth isn't quite a sphere
Picking up an old fluids textbook, I think I have the answer: Laplace's law states that by increasing the radius of a fluid vessel, the wall tension necessary to keep the system in equilibrium also increases. Now, a sphere is the shape where you have least distance from the centre to the outermost point, i.e. that with the smallest vessel radius.
We also know that the gas pressure throughout the bubble is uniform (Pascal's law).
So, if the bubble deviates from the spherical shape, the bits that are further away from the centre of the bubble than for a spherical bubble will get pushed in (because the gas pressure is not sufficient to cancel out the wall tension), and the bits that are nearer from the centre will get pushed out.
Hence, the bubble finds equilibrium in a spherical shape.
The planetary one is indeed down to gravity. This one is far easier. As you know, everything tries to get to a lower state of gravitational potential energy. If you hold something in the air and let go, it falls to the earth. So, the sphere is the shape of least gravitational potential energy. Of course the Earth isn't quite a sphere
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Big_Spark
For bubbles and other spherical droplets in the atmosphgere and in vacuums it is Surface Tension that dictates the spherical shape of the form..
For Planets..it is GRAVITY that is the dictate. Above a certain size, about 60 miles, the gravity of the body will be sufficient to force the material to "flow" into a spherical shape as the body forms, as gravity pulls equally in all directions so lond as the field strength is uniform.
For Planets..it is GRAVITY that is the dictate. Above a certain size, about 60 miles, the gravity of the body will be sufficient to force the material to "flow" into a spherical shape as the body forms, as gravity pulls equally in all directions so lond as the field strength is uniform.
Where?
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funny thing is I don't do the lottery
sterling ) on the lottery but I'm not spose to tell anyone yet for security reasons so stay shtum about it cos when I get it I'm going to share it with you guys............................I know, but I really won't to do this so its just a matter of time Yeee ha !!! we is gonna party on!!!
funny thing is I don't do the lottery
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B.O.B DOLE
and i got another $1.000.000 question why do dogs smell each others bottoms
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