Why both Earth and moon must rotate about the common centre of mass rather than the moon about the centre of..

Question

Why both Earth and moon must rotate about the common centre of mass rather than the moon about the centre of mass of Earth?

Intro: Astronomical observations show that the centre of mass of the earth moon system is 4.7x10^6from the centre of the earth.

Wait a moment, I have another question! Does it means that F(Earth)=F(Moon) at the centre or the gravitational forces of attraction cancel out at the centre of mass?

but why? can you explain in more detail?? Pascal?

Anyone out there plz help

don't spam plz

Answer 1

Consider only the Earth and Moon for a moment. Imagine a rod connecting the two and then imagine spinning this arrangement in space.It will rotate about the center of mass of the works. Now imagine shortening the rod. No change. Shorten the rod until everything merges into a single mass, Again, no change. The parts all will rotate about the same center of mass. The rod is the gravitational attaction counterbalanced by centripedal force.The whole works is in orbit about the Sun where gravitational attraction is balanced by centripedal force. I think Kepler is the guy you are looking for on this. He did a lot of thinking about orbits and why planets behave as they do.

I suppose you have heard about discovering planets in orbit around other suns? One way they determined there was a planet even though it is impossible to see was the wobble in the star because the other star and planet were rotating about the center of mass of the sun/planet system, Another way is the brightness changing as the sun is eclipsed by a planet, but for this way to work, we would have to see the star in the ecliptic plane, i.e., edge-on and the planet would have to be relatively large to occlude enough of the star to see the difference as it passed between us and the star.

Answer 2

The earth and the moon are simply two masses large and close enough to have their motion dominated by their mutual gravitational attraction. If their relative velocity were higher, they would fly apart. If it were smaller, they would collide. Instead, the gravitational force on each is exactly enough to accelerate each into an orbit. If their masses were identical, the motion of each would be circular and the circles would share the same center. The same force causes the smaller mass to accelerate more. If you spin yourself with a 10-pound weight at arm's length, your motion is smaller. Do it with a 1000-pound weight, and the weight's motion will be smaller (assuming you weigh less than 1000 pounds).

Two such objects in a stable orbit, at a fixed distance with respect to each other, could be considered a single object. When that object spins, it will spin about its center of mass.

Answer 3

EDITED:



ok ok ok...for the moon to rotate about the center of mass of the earth, it would have to be a very little mass with no gravity of it's own like a sattilite from earth. But since the moon is very large but small in comparison to earth like 1/6 th of earth's mass or something close to that, its mass affects the earth's gravitational pull and the equilibrium of the two bodies lies at the center of mass of the whole system. So like i said earlier, for the moon to be orbiting the earth about our center of mass, it would have to be one with the earth itself, but since the gravity of the earth is pulling on the moon, and the gravity of the moon is pulling on the earth they both meet at the comprimising postion with is called the center of mass of the system where the two bodies are held in equalibrium in space.

do u get it?

Answer 4

moon rotates about the earth because of the gravitational force of earth on moon (because earth is a heavier particle than moon.)earth and moon are at the same distance from sun (the distance between earth and moon is negligible due to great distance between earth and sun ) therefore the commen or reduced mass of earth and moon revolves around the sun.

Answer 5

I save in concepts from physics that the middle of mass is slightly decrease than the earth's floor. i trust this is something about 2 hundred miles down, yet do not save in concepts for particular. also, the moon would not revolve round the Earth, they both revolve round this effortless middle of mass. i recognize that would not answer the entire question, yet a minimum of it really is a initiate.

Answer 6

Because the moon also has gravity.

Answer 7

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