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The Earth revolves around the Sun and a satellite also revolves around the Earth. The Sun has a gravitational effect on all celestial bodies, so does it also have an effect on the satellite? If so then can we say that the net force on a satellite revolving around the earth is not equal to zero?

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    $\begingroup$ Please, could you explain the last sentence? In which reference frame the net force on a satellite would be zero? $\endgroup$ Dec 6, 2023 at 8:04
  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Dec 6, 2023 at 9:07

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Is a satellite revolving in Earth's orbit also affected by the gravity of the sun or other planets ?

Yes it is. For a satellite in a low Earth orbit, the largest effect will be the Earth's gravity, but it will also be affected by the gravity of the Sun and of the Moon, and (to a much smaller extent) by other planets too. For a satellite further away from Earth, such as the James Webb Space Telescope, the effect of the Sun's gravity may be as great or grater than the Earth's.

Can we say that the net force on a satellite revolving around the earth is not equal to zero ?

Yes, but even without taking into account the Sun or the Moon, the net force on a satellite in orbit around the Earth is not zero anyway. If the net force on the satellite were zero then it would travel in a straight line at a constant speed (due to Newton's First Law) so it would not be in orbit.

In a comment you suggest that net force on the satellite must be zero if its angular momentum is conserved. This is not correct. Its angular momentum about the centre of the Earth is conserved if there is no net torque acting on it - zero torque is not the same as zero force. Since the direction of the gravitational force is through the centre of the Earth (as long as we omit the effect of the Sun, Moon and other planets) then its torque (about the centre of the Earth) is always zero. So the angular momentum of the satellite is constant even though there is a non-zero net force acting on it.

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  • $\begingroup$ Thanks , to erase my confusion of first question but if net force on a satellite revolving around the earth is not zero then why it's angular momentum is conserved , as we always learn in gravitational study same in reference to earth and sun $\endgroup$ Dec 7, 2023 at 18:54
  • $\begingroup$ @VidushiAggarwal The angular momentum of the satellite is conserved if the net torque acting on it is zero. Zero torque is not the same as zero force - I have added a paragraph to my answer to explain this. $\endgroup$
    – gandalf61
    Dec 8, 2023 at 9:14
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Definitely it is, even you're experiencing an uncountable number of gravitational or electromagnetic forces right now, every particle around the universe is subjected to experience gravitational force from every other, and it's just about the magnitude which decides the major deformation a system of particle may face in it's geometry or trajectory.

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