This is College Physics Answers with Shaun Dychko. As the Earth orbits the Sun, the dominant force involved is gravity because gravity is pulling the earth towards the sun. As the sun scoots at the side, the gravity is changing direction to always towards the sun so it's always radial, that part remains the same. In the the Cartesian two-dimensional plane, the direction is changing so that's always perpendicular to the velocity of the earth. But in any case, we're trying to explain why gravitational force is the dominant force and the distance between the Earth and the Sun is large. That means the strong nuclear force and the weak nuclear force cannot apply over such a large distance. The Earth and the Sun are, for the most part, electrically neutral and so the electrostatic force is not going to apply. That means the only remaining fundamental force is gravity and it does apply on account of the masses involved, that of the Sun and the Earth being so large.
Describe a situation in which gravitational force is the dominant force. Why can the other three basic forces be ignored in the situation you described?
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