How Does Gravity Influence the Movements of Planets and Moons?

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Discussion Overview

The discussion revolves around the influence of gravity on the movements of planets and moons, specifically focusing on the Earth-Moon system and the Earth's orbit around the Sun. Participants explore the nature of gravitational forces, orbital mechanics, and the implications of these forces on the distances and interactions between celestial bodies.

Discussion Character

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

Main Points Raised

  • One participant questions why the Moon is pulled by the Earth and does not move freely, and whether the gravitational force of the Sun affects the Moon similarly to the Earth.
  • Another participant explains that gravity is the attraction between masses and that the orbits of the Earth and Moon are a result of gravitational attraction balanced by their velocities.
  • It is noted that the Sun's gravitational influence does interact with the Moon's orbit, but this effect is relatively small compared to the Moon's natural elliptical orbit.
  • One participant asserts that tidal interactions are causing the Moon to slowly move away from the Earth, indicating that a collision is not a concern.
  • Another participant argues that there is only one force, gravity, acting between the Earth and Moon, providing the necessary centripetal acceleration for the Moon's orbit, while describing centrifugal force as an apparent force.

Areas of Agreement / Disagreement

Participants express differing views on the nature of forces acting between the Earth and Moon, particularly regarding the role of centrifugal force. While some agree on the gravitational interactions, there is no consensus on the characterization of forces involved.

Contextual Notes

Participants mention the complexity of orbital mechanics and the variations in the Moon's distance from the Earth, but do not resolve the specifics of these interactions or the implications for future movements.

Redi
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Why do specific object movement is conditioned by the gravity force? Why the moon is pulled by Earth and doesn`t move freely? Why the planets don`t move in different way but obey to the gravitacional force of Sun? Everybody knows that Earth moves around the sun for 1 year and travels for hundreds of kilometres.The moon moves together with the Earth in this 1 year trip. What is the force that comands the Moon to stay with Earth and don`t leave it? And does the gravitacional force of Sun affect Moon as same as it affects Earth? Moon and Earth pull each-other and move under the affect of gravity of Sun . Is there a force that keeps them in a specific distance from each-other or they will pull each-other for a long time until they maybe crash? I think gravity of Sun made Moon come closer to Earth and than caused this year catrastophy in Japan?
 
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Gravity is the attraction matter to matter. for two objects it is proportional to the product of the objects' mass divided by the distance between the objects' centers.

The Earth orbits the Sun and the Moon the Earth because of a balance between the gravitational attraction and the the tendency for them to travel in straight line due to their velocities. The Earth, left to itself would fly off in a straight line at -30 km/s. The pull from the Sun curves this path into an orbit. The same goes for the Earth and Moon.
The exact details of these orbits is fairly complex and a field of study in of itself.

The Sun does interact with the Moon's orbit as do, to a much smaller degree, other planets in the solar system. This tends to stretch and compress the Moon's orbit slightly. However, this is a fairly small effect and is dwarfed by the fact that the Moon's orbit is naturally elliptical to start with and its distance from the Earth varies over the course of a month. This causes a variation in the tides.

Tidal interaction between the Earth and Moon is actually increasing the distance between the Earth and Moon, so there is no fear that the Moon will ever crash into the Earth.

In short, the Moon hasn't done anything beyond what it has been doing naturally for millions of years, nor do we have any reason to expect it to in the future. So, no, the Moon did not have anything to do with the Japan Earthquake.
 
Redi said:
. Is there a force that keeps them in a specific distance from each-other or they will pull each-other for a long time until they maybe crash??



Two forces

1. Gravity = pulling at each other
2. Centrifugal force = trying to move away from each other

Keeps them at a safe distance.

BTW
The moon is slowly moving away from the earth. So in the far future it will be significantly farther from Earth than it is now.
 
@Radrook

No - there's just one force, that of gravity, between Earth and the Moon, and it supplies the centripetal acceleration needed to keep the Moon in its orbit around the Earth.

Centrifugal force is an apparent force due to centripetal acceleration.
 

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