Why does the earth have a force of gravity?

Correct answer: D. In short, the gravity on earth comes from its mass. All masses will have their own gravity. The bigger the mass, the stronger the gravity. We calculate this using Newton’s formula for gravity which states F = Gm/r^2. This is why B is incorrect. We certainly know why gravity exists, and we have already calculated it — it’s 9.81 m/s^2. While the sun does influence the earth, it is not the CAUSE of earth’s gravity. The force of the sun mainly makes the earth spin around the sun. While A might sound correct, everything in physics exists for a reason! In this case, Earth’s gravity exists because of the earth’s mass.