When an object is big enough that gravity wins - overcoming the strength of the material from which the object is made - it will tend to pull all the object’s material into a spherical shape. This, incidentally, is why you don’t have to worry about collapsing into a spherical shape under your own gravitational pull - your body is far too strong for the tiny gravitational pull it exerts to do that.Ĭurious Kids: how and when did Mount Everest become the tallest mountain? And will it remain so? Smaller solid objects (metres or kilometres in diameter) therefore have gravitational pulls that are too weak to pull them into a spherical shape. An object must be really big before it can exert a strong enough gravitational pull to overcome the strength of the material from which it’s made. Areas where the water was unusually low would be filled up by water displaced from elsewhere, with the result that this imaginary ocean Earth would become perfectly spherical.īut the thing is, gravity is actually surprisingly weak. Any areas where the water was unusually high would sink, pulled down by Earth’s gravity. If Earth were made entirely from ocean, Mount Everest would just sink down all the way to Earth’s centre (displacing any water it passed through). The extra weight will push the mountain down into Earth’s mantle, limiting how tall it can become. As Everest gets taller, its weight increases to the point at which it begins to sink. Think of a great mountain, such as Mount Everest, getting larger and larger as the planet’s plates push together. That’s because the ground pushes back up at you it has too much strength to let you sink through it. For instance, the downward force you experience due to Earth’s gravity doesn’t pull you into the centre of the Earth. The bigger something is, the more massive it is, and the larger its gravitational pull.įor solid objects, that force is opposed by the strength of the object itself. An object’s gravitational pull will always point towards the centre of its mass. The answer to why the bigger objects are round boils down to the influence of gravity. Bigger objects are round, but the small ones are anything but! Wikipedia/Antonio Ciccolella Gravity: the key to making big things round … A variety of the Solar System’s small bodies, to scale.
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