|How much does the earth weigh?.|
Or what is the same: 6,600 trillion tons is the weight or, rather, the mass of the earth, as estimated in 1798 by the English physicist Henry Cavendish.
As it was evident that he could not take the planet and place it on a scale, he achieved this result through an idea that was provided by the law of universal gravitation of Isaac Newton.
He said that every body in the universe attracts another with a force that depends on mass, distance and a universal gravitation constant whose value, until then, was unknown.
To carry out his experiment he had the following idea: he suspended a weight bar from a rope in half and placed lead balls next to each of them. It was called the torsion balance experiment or Cavendish experiment.
Cavendish managed to find out the value of the gravitational constant from the masses of weights and balls and the oscillation of the weights. And the next step: as the diameter and the force of attraction of the Earth were already known at that time, it was easy to calculate its mass with the help of the gravitational constant.
Cavendish made numbers. Result: the Earth weighed 6,600 trillion tons, that is, 6,600,000,000,000,000,000,000,000 kilos. Modern measuring satellites, whose orbit also depends on the mass of the Earth, have shown how accurately Cavendish worked two centuries ago, despite its rudimentary instruments.
The value calculated by the English physicist has only needed a correction of ten percent. Today we know that our planet weighs exactly 5,975 trillion tons. What we have not been told is whether this weight is with people on or without it.