Orbit of Moon and the earth around thier COM

In summary, it is believed that the moon orbits the center of mass of the earth-moon system. This causes the distance between the Earth and Moon to vary, resulting in different tidal forces and a slight wobble in the Earth's path. While the angular velocity of the orbit may remain constant, the distances between the two bodies are constantly changing, leading to varying forces applied by each on the other. This idea was confirmed by Stonebridge and can also be found through a simple Google search.
  • #1
hms.tech
247
0

Homework Statement



does the moon orbit the Earth or the Center of mass of the earth-moon system.


2. Relevant ideas
well, i think that it orbits the COM of the earth-moon system.



If this is the case then is the radius of the moon from the Earth always constant.
ie, if the moon orbits the COM of this system then the Earth must also orbit the COM of the system, hence the distance of Earth from the moon would always be changing and therefore the force applied would be changing too.
 
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  • #2
I think your in the right mindframe. They both orbit the COM. It is just that the COM is located within the Earth, so that makes the moon orbit at different distances. Hence, from that deduction, this would also cause a small womble in the Earth as its orbit around the COM would be a smaller tighter orbit. You are right about the different forces. This is apparent with the different tidal forces that cause the rise and fall of the oceans on Earth. Any other questions or discussions?
 
  • #3
the distances are not changing,they have the same distance from COM and from each other.both of them are rotating around COM with same angular velocity,so their distance won't change,
go0d luck
 
  • #4
The moon's orbit is not regular. There is a perigee and apogee whereby the distance between the Earth and Moon varies considerably during its orbit. This in turn means the distance of both Earth and Moon from the CoM varies.
The c of m is in orbit about the Sun which gives rise to a slight wobble in the Earth's path.
 
  • #5
armin.hodaie said:
the distances are not changing,they have the same distance from COM and from each other.both of them are rotating around COM with same angular velocity,so their distance won't change,
go0d luck

if u are referring to the equation : F=mrw^2

then even if the angular velocity (w) is constant(ie moon taking a constant no. of days to complete it's different phases) but still we can conclude (using simple maths) that distances are changing:

as i have already "asked" :
Assuming that the angular velocity is constant, would the radius change as the moon and the Earth orbit each other?

and if that ^^ is to happen then another thing must change too ie force applied by the Earth on the moon and the reaction force applied by the moon on the earth.

which is already answered in post no.2, so i would like further confirmation about post no.2

what he said , was it all correct ?
 
  • #6

1. How is the center of mass (COM) of the Earth and Moon system calculated?

The center of mass of any system is calculated by taking into account the masses and distances of each object within the system. In the case of the Earth and Moon, the COM is the point at which the two objects would balance each other if they were connected by a hypothetical rod. This point is located about 4,670 kilometers from the center of the Earth towards the Moon.

2. Does the Moon always orbit the Earth at the same distance?

No, the Moon's distance from the Earth varies due to its elliptical orbit. At its closest point (perigee), the Moon is about 363,300 kilometers away from the Earth, while at its farthest point (apogee), it is about 405,500 kilometers away.

3. How long does it take for the Moon to orbit the Earth?

The Moon takes approximately 27.3 days to complete one orbit around the Earth. This is known as its orbital period, or synodic period, and is measured from one new moon to the next.

4. What causes the phases of the Moon?

The phases of the Moon are caused by the relative positions of the Earth, Moon, and Sun. As the Moon orbits the Earth, the amount of sunlight that reflects off its surface changes, resulting in the different phases we see from Earth.

5. Is the Moon moving away from the Earth?

Yes, the Moon is slowly moving away from the Earth at a rate of about 3.8 centimeters per year. This is due to tidal forces between the two bodies, which are causing the Earth's rotation to gradually slow down and the Moon's orbit to expand.

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