On Sun, Dec 2, 2018 at 11:54 PM Brent Meeker <[email protected]> wrote:
>>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. > > > > He was measuring the change in a much smaller gravitational field. > Cavendish was measuring the displacement of a torsion balance parallel to the Earth's surface caused by a weak but constant gravitational field, there was no change whatsoever in the gravitational field parallel to the Earth's surface at any time during the exparament. If he had 2 *PRECISELY* identical cannonballs on the ends of a rod, placed a pivot point *PRECISELY* at the center and place one cannonball one centimeter higher than the other he would have transformed his torsion balance into a weight balance and theoretically he could have observed that the balance moved and measured the small difference in strength in the large field at 2 different places, but Cavendish couldn't come close to achieving the sort of precision required to do that 220 years ago, we can't even do that today. > * > He was measuring the difference between the force on the torsion > balance with the cannon balls present vs absent. * > Cavendish setup the exparament but nothing moved because the torsion balance was held in place by a thread, he then sealed the room and did nothing for 2 days to let the air currents settle down. He then carefully burned through the thread freeing the torsion balance and observed its movement from far away through a telescope so his own movements wouldn't disturb anything. At no time did he measure the very small change of strength of 2 very large gravitational fields because a torsion balance can't do that, you'd need either a super good weight balance or a super good 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.
