Because Earth is suspended in space to «weigh» her – quite
not the same that to lay an object on the bowl of scales. When we speak about weight of Earth we mean the amount of matter from
which she is. It is named mass.
Mass of Earth - about 5 976 sekstyllyonov tons. That you
could evidently to imagine as this number looks here it:
5 976 000 000 000 000 000 000. How scientists counted up that mass
Earths just the same.
To do it they used the principle based on that two bodies are attracted to each other. Force of gravitation depends on it. Simpler speaking the law of gravitation says that two bodies are attracted to each other with force which depends on their mass and distance between them. Than anymore objects. That znachy-tel'nye force which attracts them to each other. Than farther from each other they are that these force less.
To measure weight of Earth it is needed to do the following: little
gruz to hang up on a filament after measure exact position of this load. Then the ton of lead is necessary to be disposed next to the suspended load. Between him and attraction is a lead as a result
which a load hardly otklanyaetsya aside (in actual fact this declination makes less than 0 000 02 mm that you see as far as measuring must be exact).
After these measuring scientists can by mathematics
to calculate weight of Earth.