Is Relative Motion Evidence of a Static Aether in Orbital Physics?

[alpha1714]

When a moon orbits around a planet, its centripetal force is balanced against the gravity of the planet, keeping it in a stable orbit. If all motion is relative, then the moon in perfect orbit could be said to be standing still while the planet rotates under it. The major difference I see is that if the moon is 'still' while the planet rotates, there would be no centripetal outward force to balance against the planet's gravity! Wouldn't it fall into the rotating planet?

Does a moon have angular momentum even if it is considered 'still' and the planet rotates? What am I missing?

I suppose the core question here is whether or not this scenario is evidence for a static 'aether', or space-time as a fabric within which absolute motion is truly applicable. Most contemporary theories reject any 'absolute' position or motion, so I'd be interested how relative motion can account for the seeming lack of congruent forces between perspectives within the physical system.

Thanks,

-alpha1714

 

[Matterwave]

Centripetal force IS the gravitational force. The gravitational force supplies the centripetal force in this scenario to keep the Moon from shooting off into space.

The reason the Moon doesn't fly into the Earth is not because the forces are balanced, but because it has sufficient velocity to escape a collision with Earth. In a sense, it is constantly falling towards the Earth, but it's "horizontal" speed is sufficient that it clear's Earth's curvature.

See this picture for example:
http://en.wikipedia.org/wiki/File:Newton_Cannon.svg

As for relative motion; since the Moon is constantly falling towards Earth, it is undergoing constant (approximately) acceleration. Thus, the Moon's reference frame is accelerated, and not inertial. Therefore, the principle of special relativity doesn't apply to the Moon. One must use general relativity to discuss these reference frames...a subject I'm not sufficiently proficient into make further discussion.

 

[TurtleMeister]

The inertial frame of reference for bodies in orbit about each other is the center of mass, or barycenter. For the Earth moon orbit, that center is located within the Earth itself. The reason for this is that the Earth is more massive than the moon. The Earth does orbit the moon, but because the center is located within the Earth itself, the Earth only appears to wobble.

Go to this wikipedia page and scroll down to the section labeled "animations".
http://en.wikipedia.org/wiki/Center_of_mass

 

[alpha1714]

Thanks everyone for your replies. After considering your posts and a lot of further pondering, I think I understand what I was missing.

From the perspective of the planet, it is standing still while the moon is revolving around it. From the moon's point of view, it is still while the planet spins beneath. In both cases, however, the gravitational acceleration toward each other is balanced against a feeling of opposite acceleration in exactly the other direction. From the perspective of the moon, it is falling toward the planet while the planet is moving directly away from the moon at the same speed, and vice versa. This accounts for the feeling of mutual attraction while remaining at a fixed distance. It's like a speedboat dragging a water skier behind, both always feeling the tug of attraction but remaining the same distance apart.

Thanks again for your help, keep up the good thinking.

-alpha1714

 

[sardar]

Thank you for your question. Relative orbital physics is a complex and fascinating subject, and I appreciate your interest in it. Let me address your concerns and questions one by one.

Firstly, you are correct in stating that the centripetal force of a moon orbiting a planet is balanced against the gravity of the planet. This is known as the gravitational force of attraction, and it is what keeps the moon in a stable orbit around the planet. However, it is important to note that this force is not the only force at play in this scenario. The moon also has its own inertia, which is the tendency of an object to resist changes in its state of motion. This inertia acts as a counterforce to the gravitational force, and it is what allows the moon to maintain a stable orbit without falling into the planet.

Secondly, you are correct in saying that if the moon is "still" while the planet rotates, there would be no centripetal outward force to balance against the planet's gravity. However, this is where the concept of relative motion comes into play. From the perspective of an observer on the planet, the moon appears to be moving in a circular orbit around it. But from the perspective of an observer on the moon, the planet appears to be rotating beneath it. This is because motion is relative, and it depends on the frame of reference of the observer. So, while it may seem like there is no outward force acting on the moon, this is only true from the perspective of an observer on the planet. From the perspective of an observer on the moon, the outward force is still present.

Now, to address your question about angular momentum. Yes, the moon does have angular momentum even if it is considered "still" and the planet rotates. This is because angular momentum is a property of an object's motion, and it is not affected by the frame of reference of the observer. In simpler terms, the moon is still moving in a circular orbit around the planet, even if it appears to be "standing still" from the perspective of an observer on the planet.

Finally, let me address your question about the concept of a static "aether" or a fabric of space-time. While these ideas were once popular in physics, they have been largely rejected by contemporary theories. The concept of relative motion and the idea that all motion is relative, rather than absolute, is supported by a vast amount of evidence and has been successfully used to explain and