Why are planets round? – Daniel B, La Crosse, Wisconsin
More than 2,000 years ago, the ancient Greeks proved that the shape of the Earth is round and they also know its size by using simple observations of the Sun.
But how do people today prove the spherical shape of the Earth? When you drop something, gravity causes it to fall straight to the center of the Earth, at least until it hits the ground.
Gravity is the force exerted by almost any object that has mass. Pulp is the amount of matter in something. Mass is in rock, water, metal, people – you name it. All matter has mass, and therefore everything causes gravity. Gravity always pulls towards the center of mass.
Earth and all planets are round because planets when formed consists of a liquid material – basically a very hot liquid. Since gravity always points toward the center of mass, it pushes the material evenly from all directions to the center, forming a sphere. When the Earth cools and becomes solid, it forms a round ball. If the Earth did not rotate, it would form into a perfectly round planet. Scientists call something that is perfectly round in all directions a “sphere”.
The gas cloud on which the Earth was formed slowly rotates in one direction around its axis. Top and bottom These axes are Earth’s north and south poles.
Try extending your right hand. Point the thumb on your right hand straight up, and bend your fingers around the direction of rotation. Your thumb points towards the North Pole. The equator is defined as the plane halfway between the North and South Poles.
–Todd Warnock/DigitalVision via Getty Images
If you’ve ever played in carousels, you know that spinning carousels often leave you feeling thrown up. The faster the merry-go-round, the harder it is for people to survive. This feeling of being thrown away is called centrifugal force and pushes the mass at the equator away from the midpoint. This is what makes the planet stand out at the equator.
The faster the planet spins, the less round it becomes. Then, as it cools and hardens, it will hold on to that shape. If a liquid planet started spinning faster, it would become less round and have a larger bulge.
Planet Saturn very flat – not round – because it rotates very fast. By gravity, all planets are spherical, and because they rotate at different speeds, some have a fatter equator than the poles. So the shape of the planet and the speed and direction of its rotation depend on the initial conditions of the material that formed it.
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Rachel Noorajavi translated this article from English.
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