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Question
Consider four forces: the gravitational force between the Earth and the Sun; the electrostatic force between the Earth and the Sun; the gravitational force between the proton and electron in a hydrogen atom, and the electrostatic force between the proton and electron in a hydrogen atom. What is the proper ordering of the magnitude of these forces, from greatest to least?
  1. gravity, Earth-Sun; electrostatic, Earth-Sun; gravity, hydrogen; electrostatic, hydrogen
  2. electrostatic, Earth-Sun; gravity, Earth-Sun; electrostatic, hydrogen; gravity, hydrogen
  3. gravity, Earth-Sun; gravity, hydrogen; electrostatic, hydrogen; electrostatic, Earth-Sun
  4. gravity, Earth-Sun; electrostatic, hydrogen; gravity, hydrogen; electrostatic, Earth-Sun
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Final Answer
(d)
Solution Video

OpenStax College Physics Solution, Chapter 33, Problem 3 (Test Prep for AP® Courses) (1:20)

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Video Transcript

This is College Physics Answers with Shaun Dychko. We need to sort four forces into order from greatest to least and the question is intentionally trying to be a bit tricky; we have been told in this chapter that gravity is such a weak force in comparison to the other forces but it turns out in this question, it is the strongest force because the Earth and Sun are so massive that gravity is nevertheless giving the greatest force among these four possibilities. The electrostatic force in a hydrogen atom is the next largest force because the proton is tightly binding the electron into orbit around it. And gravity with the hydrogen where does it say exactly gravitational force between the proton and an electron well, there's very little of that because the proton and electron are so light such small mass and so gravity between the sub-atomic particles is going to be smaller and then the smallest force here will be any electrostatic force between the Earth and the Sun because these objects are not charged and they are very far apart and so this is the weakest.