Why are all the orbits elliptical and not circular?

In summary, in high school, the terms centrifugal and centripetal force were used to explain the orbits of planets and satellites. However, even circular orbits are technically elliptical. The real question is why eccentricity is never zero, and this is due to various factors such as the starting situation and interactions with other objects. Kepler's First Law describes planetary orbits as ellipses, while circular orbits are more difficult to achieve. Conservation of angular momentum and inverse-square central forces also play a role in determining the shape of orbits. This has nothing to do with relativity.
  • #1
Monsterboy
303
96
In high school whenever i asked questions about planets and their orbits around their star or the orbits of satellites around their planets ,i always got the answers with the terms centrifugal ,centripetal force and an example of a stone tied to a thread and how it behaves when you hold the thread at the other end and by swinging it, you make the stone orbit your fist but this circular not elliptical but all things that i mentioned about move in elliptical orbits ,even electrons revolve around the nucleus in elliptical orbits right ? i never got the answer for my "elliptical question" .can i get an answer please? maybe my teachers thought that it was too complicated for me to understand because i didn't know about relativity or something?
 
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  • #2
Electrons don't orbit in the classical sense.

A circle is a special case of an ellipse (with zero eccentricity) so even a circular orbit is elliptical. So the real question should be why is eccentricity never zero? Well that would require an absolutely perfect starting situation and no interaction with other objects to disturb that perfection later.
 
  • #4
Circular orbital motion is a unique set of circumstances - exactly the right speed, distance from the central body, angle of the "flight path". Change any of these, and you no longer have the right combination. Imagine that, rather than swinging it around in a circle, you let the stone dangle - a pendulum - you can get it to swing back and forth in a straight line, or around in a circle, but neither is easy. It's very easy to get it to swing in random more or less elliptical loops. Ellipses are the typical, easy, normal condition - circles are atypical, difficult, unusual.
 
  • #5
Circular orbits are virtually impossible save for the case of two body systems. Even then they are subject to distortions due to density anisotropies - not to mention gravitational influences by remote bodies.
 
  • #6
If you were to phrase this "why do not all orbits have eccentricity exactly 0.000...", I think it would be easier to see.
 
  • #7
Hi Monsterboy! :smile:

Central orbits (ie where the force is always towards a fixed centre) have to obey conservation of angular momentum, which gives you Kepler's equal-areas-in-equal-times law.

If the central force is inverse-square, then we can prove that the orbit must be an ellipse, and yes, your high school teacher was probably right in thinking that you wouldn't understand the maths! :wink:

(but it has nothing to do with relativity)
 

1. Why are all orbits elliptical and not circular?

It is a common misconception that all orbits are circular. However, all orbits are actually elliptical in shape. This is due to the gravitational pull of the central body, which causes the orbiting object to follow an elliptical path.

2. How does the shape of an orbit affect the motion of an object?

The shape of an orbit can greatly affect the motion of an object. In an elliptical orbit, the object will experience changes in velocity and gravitational pull as it moves closer or farther away from the central body. This results in variations in orbital speed and distance from the central body.

3. Can an orbit ever be perfectly circular?

In theory, an orbit can be perfectly circular if the central body has a perfectly even distribution of mass and there are no external forces acting on the object. However, in reality, this is impossible to achieve. Even the slightest asymmetry in the distribution of mass or external forces will cause the orbit to become elliptical.

4. Are all planets in our solar system on elliptical orbits?

Yes, all planets in our solar system follow elliptical orbits around the Sun. However, these orbits are very close to being circular, which is why they may appear circular to the human eye. The eccentricity (or roundness) of the orbits varies among the planets, with some being more elliptical than others.

5. How do scientists determine the shape of an orbit?

Scientists can determine the shape of an orbit using mathematical equations and observations of the object's position over time. By measuring the distance and velocity of the object at different points along its orbit, they can calculate the eccentricity and determine whether the orbit is elliptical or circular.

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