Center of mass and planetary motion

In summary, the conversation discusses why the Earth and the moon orbit their common center of mass instead of the Earth's center. The analogy of a dad swinging his daughter around is used to explain the concept of center of mass. The link provided by one of the speakers offers a detailed explanation of the two-body problem.
  • #1
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Why is it that for instance the Earth and the moon orbit their common center of mass? I mean surely the moon feels a gravitational force as though the mass of the Earth were concentrated at its center? If yes, what is that then makes it orbit around their center of mass rather than this point. I do realize that the Earth will also feel a gravitational force from the moon, but I still don't really see it. Can you explain this intuitively and do any of you have a link that might explain it well?
 
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  • #3
Imagine a dad swinging his little girl around in a circle. He has to lean backwards a little bit in order to avoid falling over. The "center of mass" for this scenario is no longer inside either of the two people, just like it isn't exactly in the middle of the Earth or the Moon. The article mathman linked will explain it in detail.
 

Related to Center of mass and planetary motion

1. What is the center of mass?

The center of mass is the point at which all the mass of a system can be considered to be concentrated, and the system will behave as if all the mass is located at that point.

2. How is the center of mass related to planetary motion?

The center of mass is an important concept in planetary motion as it is the point around which planets orbit. The center of mass is also used to determine the gravitational forces and movements of planets.

3. Is the center of mass always located within the planet?

No, the center of mass can be located both inside and outside of a planet. For example, the center of mass of the Earth and Moon system is located inside the Earth, while the center of mass of the Pluto and Charon system is located outside of both bodies.

4. How does the center of mass affect the stability of a planetary system?

The center of mass plays a crucial role in the stability of a planetary system. If the center of mass is located far from the center of the planet, it can cause the planet to wobble or even become unstable in its orbit. This is seen in the case of Pluto and its moon Charon, where the center of mass is located outside of Pluto and causes its orbit to be constantly changing.

5. Can the center of mass change over time?

Yes, the center of mass can change over time, especially in systems with multiple bodies. As planets and other celestial bodies interact with each other, their positions and masses can change, causing the center of mass to also shift. This is seen in the case of the Earth and Moon system, where the Moon's orbit is gradually moving further away from the Earth, causing the center of mass to also shift.

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