Earth's Path: Why Ellipse? - How Come, Why Not Circular Motion?

  • Context: High School 
  • Thread starter Thread starter Bassalisk
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Discussion Overview

The discussion revolves around the nature of Earth's orbital path around the Sun, specifically questioning why it follows an elliptical shape rather than a circular motion. Participants explore concepts related to energy conservation, orbital mechanics, and the conditions required for different types of orbits.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question why Earth follows an elliptical orbit instead of a circular one, suggesting that changing speed implies changing energy and acceleration.
  • Others explain that as Earth moves closer to the Sun, it gains kinetic energy, which is balanced by gravitational potential energy, maintaining total energy conservation.
  • One participant argues that a circular orbit would be simpler and questions the necessity of an elliptical path.
  • Another participant states that circular orbits are nearly impossible due to the need for precise initial velocity, leading to elliptical orbits as a more likely outcome.
  • Inertia is mentioned as a factor, with a participant suggesting that the Sun's gravitational pull causes the elliptical orbit.
  • There is a technical explanation regarding the conditions for circular, parabolic, and hyperbolic orbits, emphasizing the low probability of achieving the exact speed needed for circular motion.

Areas of Agreement / Disagreement

Participants express various viewpoints on the nature of Earth's orbit, with some agreeing on the mechanics of energy conservation while others question the implications of an elliptical path versus a circular one. The discussion remains unresolved regarding the necessity and implications of the elliptical orbit.

Contextual Notes

Participants highlight the dependence on initial conditions and the specific velocities required for different types of orbits, noting that achieving a perfect circular orbit is highly improbable.

Bassalisk
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Why ellipse? How come? Why not circular motion? If the path is changing, then the speed is changing, if the speed is changing it means acceleration, if u have acceleration u need extra energy, but Earth doesn't get one..
Thanks
 
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Bassalisk said:
Why ellipse? How come? Why not circular motion? If the path is changing, then the speed is changing, if the speed is changing it means acceleration, if u have acceleration u need extra energy, but Earth doesn't get one..
Thanks

When the Earth is closer to the sun it is moving faster, and therefore has more kinetic energy than when it is further away, so the total energy stays the same, as kinetic energy gets transformed into gravitational potential energy and vice versa.
 
Vagn said:
When the Earth is closer to the sun it is moving faster, and therefore has more kinetic energy than when it is further away, so the total energy stays the same, as kinetic energy gets transformed into gravitational potential energy and vice versa.

But why does Earth do this? Isn't it more simple for "her" to just have the same energy over and over ?
 
Energy is conserved in an elliptical orbit.

Circular orbits are essentially an impossibility. Any deviation of orbital velocity from that required for a circular orbit will result in an elliptical orbit.

A much better question is "why is the Earth's orbit so close to circular?"
 
Well other thing that crossed my mind, is inertia. A body wants to go in a straight line right? But sun pulling the Earth and makes orbit elliptical? Is this is it?
 
To have a perfectly circular orbit, then your body initially needs to have exactly the right speed, if this speed is more than the speed for circular motion, but is less than the larger body's escape speed, then the smaller body will undergo an elliptical orbit, if it is equal to the escape speed, then the body will move along a parabolic orbit. Finally if it is greater than the escape speed then it will follow a hyperbolic orbit. Both para and hyperbolic orbits would cause the smaller body to leave the system.

To have exactly the right speed for either parabolic or circular orbits have a very low probability. i.e. 0 chance of occurring.
 
Vagn said:
To have a perfectly circular orbit, then your body initially needs to have exactly the right speed, if this speed is more than the speed for circular motion, but is less than the larger body's escape speed, then the smaller body will undergo an elliptical orbit, if it is equal to the escape speed, then the body will move along a parabolic orbit. Finally if it is greater than the escape speed then it will follow a hyperbolic orbit. Both para and hyperbolic orbits would cause the smaller body to leave the system.

To have exactly the right speed for either parabolic or circular orbits have a very low probability. i.e. 0 chance of occurring.
I get it now, thanks!
 
Last edited:

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