What is the closest planet to the sun? Why are the planets closest to the sun rocky? Why is earth closest to the sun in January? Why is Mars closest to the Earth in August? What is accretion, and how did it form the Earth?
How does accretion explain planet formation? How does accretion form planets? See all questions in The Planets. Does gravity causes elliptical orbits? If it is true,please explain it. Yes, gravity does cause elliptical orbits. Specifically, two properties of gravity lead to the ellipse: 1.
It always points toward a fixed point 2. The strength goes inversely with the square of the distance from that point. These are not unique to gravity. An electrical force can give the same shape of orbit. Although Newton demonstrated this mathematically over years ago, it still remains hard to show. I didn't ever go through the argument in detail until well into adulthood.
Even in compact form, it's too long for this site, and at any rate it's always hard for me to reproduce it. Here's a link to a version of the argument, which the author picked up from Feynman. Additionally, the angular speed must be such that the centrifugal force in the corotating frame exactly balances the gravitational force--a little more or a little less, the imbalance will change the radial velocity, spoiling the circle.
Given the fact that velocities vary for a large number of reasons, it's no wonder that only a few orbits end up being circular, and considering that actual orbits change with time , we know they can't stay this way for long.
If you're looking for a mathematical proof, this link shares some details about it. Here's an image showing eccentricity of some bodies in the solar system extracted from here :. I always prefer answers which try to avoid any formula and reply on argumentation instead. Concerning the part of the question why not all orbits are circular, an argumentation would be like this:. Consider a stationary star and a moving planet.
For each impulse the planet can have, a curve for its further movement can be predicted. If this impulse is directed exactly orthogonal to the line from the star to the planet, and if the velocity has the exact amount , then this curve of movement can be an exact circle. So, one can simply argue, a circle is a very special case for the curve a planet can take around a star.
This answer is addressed at the level of the question for learners not professionals. Because our solar system planets travel in near circles people imagine that is somehow the natural condition. But it is a tricky question. First, we should imagine gravity as an upturned trumpet shape and a planet as a ball rolling along such surface. Depending on the direction and speed that you give the ball the trajectory will fall with a tendency to curve inwards but also speed up and so will then swing around and shoot out again then later slow down and curve back in again.
In general Newtons maths shows you get ellipse for an individual planet orbit and circle is one special ellipse. However, because of how solar system originate from gravitational collapse of giant gas and dust cloud the material tends to get herded into circular swirl much like a hurricane and planets condense by accretion in near circular paths.
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