On Sun, Dec 2, 2018 at 11:54 PM Brent Meeker <meeke...@verizon.net> 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 everything-list+unsubscr...@googlegroups.com. To post to this group, send email to firstname.lastname@example.org. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.