How was the mass of the earth measured?

Question

What is the technique applied to measure the mass of something as big as a planet?

Answer 1

The masses of planetary bodies are usually measured by analyzing the effects of gravity. For example, the period of a moon's orbit about a planet depends on the distance between them and on the masses of the bodies. So learning the period of an orbit lets us make very good approximations of the mass of the objects involved, assuming we can also measure the distance between them.

Since we live on the Earth and can easily make Earth-based observations, we can also use the known acceleration due to gravity at the surface of the Earth to calculate the Earth's mass, since we know the Earth's radius (conseriably easier to directly measure than its mass).

Answer 2

As mentioned, you can measure the acceleration due to gravity, or you can measure the Moon's orbit. No matter how you do it, you need the constant G from Newton's equation (f = GMm/r^2).

This is why we can determine the masses of planets precisely if they have moons, but must use more indirect methods when they don't. This was part of why people got so excited when they discovered Pluto's first moon Charon, because it gave the first real figures on Pluto's mass.

Answer 3

Wikipedia-geometry is a help, but you'll need to figure things through. The size of the Earth has been known since ancient times, the math is fairly simple, just multiply to get bigger answers. Once you know the size/volume, then multiply a small mass of 'earth' by that number and you'll come close to the actual mass, or weight. Good luck with your figures.

Answer 4

It was submerged in a large beaker and the displacement of the water was measure to determine the approximate mass.