Physics
The Moon

# If the moon were twice as far from the earth as it is today how would the gravitational force it exerts on the earth compare with the force it exerts today?

567 ###### 2009-08-12 18:46:58

The mutual gravitational force between two objects is inversely proportional to the square of the distance between their centers of mass. That goes for any two objects in the universe, regardless of their relative size or mass, the distance between them, how they're moving, or where in creation they're located. So if the distance between the earth and moon were doubled, the mutual force between them would change by a factor of ( 1 / 22 ) = 1/4 Each body would experience a force directed toward the other one, equal to one fourth of what the force is now.

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## Related Questions Any two objects with mass will have a gravitational force. The orbit of planets around stars depends on the gravitational pull of the star. The Earth exerts a gravitational pull on its moon but the moon also exerts a pull on the Earth. The Earth exerts the greatest gravitational force on you because it is the most massive object you are closest to. The Earth exerts a force equal to your weight. The other objects exert gravitational forces but are not very noticeable because they are either low in mass or separated from you by great distance. Newton's third law states that when a body exerts a force on another body then the second body also exerts an equally large force on the first, but in the opposite direction.In the case of the Earth and the Moon, the Earth exerts a gravitational force on the Moon of magnitude F=GMm/r2, where M is the mass of the Earth, m is the mass of the Moon, r is the distance from the Moon to the Earth and G is a constant. This force acts from the Moon towards the Earth. Likewise the Moon exerts a gravitational force on the Earth of magnitude F=GMm/r2, which is exactly the same, but this one acts from the Earth towards the Moon.So here we have two forces of equal magnitude, similar nature (both of gravitational origin) and opposite direction. Hence the reaction force of the Moon on the Earth is the force of the Earth on the Moon. The object with the most mass, as gravitational force is dependent on mass. Therefore the bowling ball exerts more gravitational force than a baseball or a football. The mass of the Earth can be determined by the gravitational force it exerts on any object. This works, once the gravitational constant is known. The gravitational constant can be measured with a Cavendish balance. Any body with mass exerts a gravitational force proportional to mass.This force is always attractive. So earth attracts all things. There is both gravitational and magnetic force associated with the earth. The mass of the earth gives rise to gravity, and magneto action in the core generates the magnetic field that moves compass needles.

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