How have scientists discovered the density of the earth?
Unfortunately, this is not a value which can be measured directly (such as the density of a rock or a potato, for example). Therefore, we can only use indirect observations.
The overall density of the earth is actually fairly easy to calculate: if density equals mass divided by volume, and we can find the mass and volume of the earth, the math is simple. Well, the volume is easy - we can easily arrive at a radius for the planet, and get the volume from the equation:
V=4/3 X pi X r3
But how do we get mass? This is a bit tougher, and relates to the earth's gravitation attraction on various objects: you, me, the moon, and so forth. We need to use Newton's formula for gravitation:
G=m1 X m2 / d2
In this case, G is the gravitational attraction between any two objects (like the earth and moon), m1 is the mass of the earth, m2 would be the mass of the moon, and d is the distance between them. Solve for m1 and we have the mass of the earth.
Now, plug both values into the equation:
D = m / v
...and we have a value for the overall density of our planet. Pretty slick, huh?
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