Why are the earth and other planets round?

Answer 1

The sun, planets, and generally speaking any very massive contiguous object tends towards a spherical shape because of rules of gravity and matter dynamics. A sphere is a stable shape in a situation where such masses evidence collective behavior of lots of particles of matter all attracting each other; it has said to have reached an equilibrium of forces called hydrostatic equilibrium. One way of thinking about this is, if you were on a plain of matter which was flat and level and the pull of gravity was downwards and perpendicular to the plain, the pressure below the surface would be the same at any given depth. However, if you were to put a mountain on that plain, the pressure would be much greater below the mountain than the surface of the plain. If it were free to move, it would tend to be flattened by gravity until irregularities were evened out; valleys would tend to seem to push up and hills would tend to flow down until the equilibrium was achieved. For a liquid or gas this happens much more quickly than a solid, but even the latter will tend towards this hydrostatic equilibrium over long periods. Note also that rotational effects also slightly flatten such spinning objects; the Sun, gas giants, other planets which rotate on their own axis are said to be oblate spheroids with the equatorial diameter slightly bigger than the polar.

Answer 2

Round is the best shape to go through the universes atmosphere. Planets are shaped by their spatial influences, pressure and outer atmospheric conditions that we do not yet fully understand!

(Correction)- First of all not all planets are round, though most non-round bodies are moons or asteroids rather than planets. Planets that are round, however, are round because of gravity. Take the Earth for example. Gravity is an inward force, pushing from all angles towards the core, so it is in affect "squeezing" the planet into a sphere. This causes any big lumps (mountains for instance) to be made flat. Of course there are mountains, but if there is a limit to how tall they may be, which is different on each planet.-Akilae
First of all not all planets are round (and none are perfectly round), though most non-round bodies are moons or asteroids rather than planets. Planets that are round, however, are round because of gravity. Take the Earth for example. Gravity is an inward force, pushing from all angles towards the core, so it is in affect "squeezing" the planet into a sphere. This causes any big lumps (mountains for instance) to be made flat. Of course there are mountains, but if there is a limit to how tall they may be, which is different on Each planet.
because god made it be that way

(Correction)-Though I personally do not dispute the existence of a god, I doubt that answer will get you far on your science homework. First of all not all planets are round, though most non-round bodies are moons or asteroids rather than planets. Planets that are round, however, are round because of gravity. Take the Earth for example. Gravity is an inward force, pushing from all angles towards the core, so it is in affect "squeezing" the planet into a sphere. This causes any big lumps (mountains for instance) to be made flat. Of course there are mountains, but if there is a limit to how tall they may be, which is different on Each planet.-Akilae
Gravity is the key. You may be aware that Jupiter, our largest planetary neighbor in the solar system, is almost all gas (there is a small core of non-gaseous material). Understanding that Jupiter is a ball of gas, wouldn't it be bizarre if it had a shape other than a sphere? Think also of a bubble blown by a child (or your inner child) through a loop. Even very large ones (which are the most fun) seem to seek rest in a spherical shape, even if breezes batter and deform it from time to time. Matter seems to seek to balance internal forces. It would be scary to look up at Jupiter and discover that it had morphed into a doughnut shape or a large tube shape.

When we are talking about collections of matter that are planet-sized, the same general idea holds. Taking a mass equal to that of the earth, and of similar materials, you could attempt in your mind to construct a pillar with a 1,000 kilometer diameter. But you wouldn't get too far before the pillar's mass would exert so much gravitational force that the whole thing would come crashing in. Even if you braced the pillar while building it, the inner sections would eventually crumble and/or melt long before you finished. Eventually, all the mass would find its way to balance out the gravitational forces

Answer 3

Because every single piece of that planet has mass and is gravitationally attracted to every other piece of the plant. The shape that arises naturally when all things are equally attracted to each other is a sphere.

Answer 4

Because they formed and collapsed under the force of their own gravity.

Answer 5

Because the most plausible and possible shape was round, due to gravitational power.