If someone involve you to librate the planet – assuming you have n’t paid much care during physics in high schooling – you might not know where to protrude . How do you librate a affair you ’re fend on ? That ’s like being asked to count your own scale without using a 2nd set of scales .
If you ’re struggle , do n’t despair . calculate out how to weigh ( well , bill themass ) of the Earth take until 1687 , and even then we could n’t work out it until 1798 .
At the final stage of the 1600s , Newton proposed the universallaw of gravitation : that every particle attracts every other subatomic particle in the universe with a force ( F ) determined by their masses ( M ) and the square of the distance between the centers of the objects ( R ) . Math fans may prefer it expressed like this : F = G(M1xM2 / D2 )
As you’re able to tell from the math , if you have the mass of one of the objects ( and all the other information within the equality ) you’re able to cypher out the mass of thesecond object . Say you were one of the known spate ( or you used a specific weight for ease ): you could calculate the exercising weight of the Earth , given that we recognize more or less how far we are from the Earth ’s center . The problem was , in Newton ’s time we did not have a time value for guanine , attain this impossible .
Newton thought that measuring the gravitational force of an object was not possible for objects smaller thanplanets and moons . However , this was not the case . lie with the mass and tightness of the Earth would be fantastically useful for astronomer , as it would aid them aim the mass and density of other objects in the Solar System , as well as it being interesting to know in its own right . In 1772 , the Royal Society set up the “ Committee of Attraction ” to fancy this out .
endeavor were made to assess the average density of the Earth using a mountain in Scotland . The squad register that the sheer slew of Schiehallion attract pendulum towards it . value the pendulum ’s campaign and surveying the mountain , they were able to figure a rough density of the Earth .
In 1797 , however , we finally set about the time value of G , allowing us to calculate the mass of the Earth . Geologist Reverend John Michell had been working on the problem , but was n’t able to finish on news report of he became dead . Instead it accrue to scientist Henry Cavendish , using Michell ’s equipment , to perform the experiment .
Using a comparatively simple-minded apparatus ( see above YouTube video fromMrLundScience ) Cavendish was able to measure the force-out between two metal area single out by a known aloofness . The gravitative violence of the Earth exert on the little ball could be measured by count it , and the denseness of the ball was also known .
Looking at the ratio between the two forces revealed the mass of the Earth , about 5,974,000,000,000,000,000,000,000kilograms(13,170,000,000,000,000,000,000,000 pounds ) , if you ’re interested .
