How do we know the mass of the earth and the moon?
Hello, I am a Biologist teaching Earth Science, I have only had 2 Astronomy courses in college. Anyways a student asked me,” How do we know the mass of the Earth and the mass of the moon?” Could you provide me with an explanation reasonable for a high school student? Thank you, I will cite your website as a resource for further questions. The Earth is the easier problem of the two. Remember that from Newton’s Law of Gravitation, (1) Fgrav. = GMm/(R^2) where Fgrav is gravitational force, G is the universal gravitational constant, M and m are the masses of the two objects attracting each other, and R is the distance between their centers of mass. Now from Newton’s Second Law, (2) F = ma where a is acceleration, F is force, and m is the mass of the accelerated object. So since we know G, all we have to do is drop an object and measure its acceleration a. Then we know F/m, which is the same as Fgrav/m since our object is moving under the influence of gravity alone. R, the radius of the Ear
