On Sun, Dec 2, 2018 at 4:29 PM Brent Meeker <[email protected]> wrote:
> *> The Earth is 3.9e22 times heavier than Cavendishes cannon ball. * > The mass of the earth is irrelevant because we're talking about measuring the difference in the strength of gravity as distance increases not its absolute value. >> In 1798 technology was good enough for Cavendish to measure the >> gravitational attraction between 2 cannonballs a few inches apart (andby >> doing so determine the value of the Gravitational Constant) but until a >> few months ago no technology was good enough to measure the difference in >> strength of a gravitational field that was 637,000,000 centimeters from the >> center of the Earth and one that was 637,000,001 centimeters from the >> center of the Earth. But the technology is good enough now thanks to >> this new clock. > > > > *N**o. The potential difference measured by the cesium clock when > raised 1cm relative to the Earth was 2.03e9 times bigger than the smallest > difference measured by Cavendish (assuming he could measure 0.00025m > deflection). The Earth is 3.9e22 times heavier than Cavendishes cannon > ball. So 300yrs ago Cavendishes technology was good enough;* If you are on the Earth's surface and you raise a clock by one centimeter you've increased its distance from the earth's center by one part in 637,000,000, it is now 1.0000000016 times further away. The intensity of the gravitational field is proportional to the square of the distance so gravity was 1.0000000031 times stronger before you raised raised the clock. Cavendish did not have a scale good enough to measure that, even today the very best (and very expensive) lab weight scale might be able to measure a change of 1.0000001 but the clock can do several hundred times better. > > (assuming he could measure 0.00025m deflection). > When Cavendish measured a deflection he was measuring the strength of the attraction between 2 canon balls, he was not measuring the difference in the gravitational field at 2 points. Cavendish used a torsion balance and its very good at measuring weak forces but it can't measure the super small difference between 2 strong forces, to do that he'd need a weight scale, or a super accurate clock. John K Clark > > > > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
