# How you Determine the Order of Magnitude of the Mass of the Earth?

*Most recent answer: 02/23/2015*

Q:

How you determine the order of magmitude of the mass of the earth?

- Dorcas (age 15)

Port Moresby,Papua New Guinea

- Dorcas (age 15)

Port Moresby,Papua New Guinea

A:

Hi Dorcas,

You know that the gravitational force between the earth and and arbitrary object is F = M_{e} m G / R_{e }^{2} where G is the gravitational constant 6.6710^{-11 }Nm^{2}/kg^{2}, R_{e} = 6.4*10^{6} m, and m is the mass of the object. You also know that the force on the object is F = mg where g = 9.8 m/s^{2} is the acceleration of an object due to the earth's gravity. Solving for M_{e} you get M_{e} = R_{e }^{2} g/G = 6*10^{24} kgm.

LeeH

And you may wonder, where did the value for G come from? Cavendish got it by measuring the gravitational force betwen two known masses. /mw

*(published on 02/23/2015)*