Planets

[Wispy68]

Why are all planets round?

[xyzzyplugh]

Earth? - an oblate spheroid.

[sft42]

TW are you sure about your reason for the "bulge in the middle"? I always thought this was caused by the speed of spin being greater at the equator therefore forcing more material of the planet outwards and the rate of gravity is surely constant at 9.81 m/s/s anywhere on the planet?? i maybe wrong on this and i stand to be corrected.

[wildwood]

The Earth bulges more at the equator and is flatter at both the North and South poles because of modifications in its gravitational pull - discovery channel.

[wildwood]

sorry, forgot to include the url: http://dsc.discovery.com/news/afp/20020805/earth.h
tml#jump

[Hamish]

Take care folks!! The discovery channel said "Could be" this is therefore stillunder debate. The reason give is to do with ralative dencities rather than variations in gravitational force and the more comon reason is that the bulge is due to the earth spinning. As to the earth being round because of a 'gravity feild', gravity acts over huge distances far more than just the surface of the earth and probably over infinite distances. The reason for roundness could be explained by think of the earth as a cooling mass of liquid. A liquid droplet of this size will form a spherical shape due to, gravity and surface tension.

I hope this answers you question.

[Jara]

Actually, gravity is only a partial answer, though an important one. A sphere is the perfect distribution of force per area, and liquids, being viscous (runny) substances, tend to distribute their weight about evenly. In a vaccum like space, where the influence of other objects on Earth is relatively small by comparrison to the Earth's own mass, this results in an almost-perfect sphere. In clouds, where falling rain drops have to contend with gravity and wind resistance, this forms anything from a 'tear drop', to a long thin streak that looks almost like a falling pin, depending on the conditions.