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i like the story more than the experiment itself. ofc, if u want to know about the experiment let me know but, here is the story: Cavendish is a book in himself. Born into a life of sumptuous privilege—his grandfathers were dukes, respectively, of Devonshire and Kent—he was the most gifted English scientist of his age, but also the strangest. He suffered, in the words of one of his few biographers, from shyness to a “degree bordering on disease.” Any human contact was for him a source of the deepest discomfort. Once he opened his door to find an Austrian admirer, freshly arrived from Vienna, on the front step. Excitedly the Austrian began to babble out praise. For a few moments Cavendish received the compliments as if they were blows from a blunt object and then, unable to take any more, fled down the path and out the gate, leaving the front door wide open. It was some hours before he could be coaxed back to the property. Even his housekeeper communicated with him by letter. Although he did sometimes venture into society—he was particularly devoted to the weekly scientific soirées of the great naturalist Sir Joseph Banks—it was always made clear to the other guests that Cavendish was on no account to be approached or even looked at. Those who sought his views were advised to wander into his vicinity as if by accident and to “talk as 4 In 1781 Herschel became the first person in the modern era to discover a planet. He wanted to call it George, after the British monarch, but was overruled. Instead it became Uranus. it were into vacancy.” If their remarks were scientifically worthy they might receive a mumbled reply, but more often than not they would hear a peeved squeak (his voice appears to have been high pitched) and turn to find an actual vacancy and the sight of Cavendish fleeing for a more peaceful corner. His wealth and solitary inclinations allowed him to turn his house in Clapham into a large laboratory where he could range undisturbed through every corner of the physical sciences—electricity, heat, gravity, gases, anything to do with the composition of matter. The second half of the eighteenth century was a time when people of a scientific bent grew intensely interested in the physical properties of fundamental things—gases and electricity in particular—and began seeing what they could do with them, often with more enthusiasm than sense. In America, Benjamin Franklin famously risked his life by flying a kite in an electrical storm. In France, a chemist named Pilatre de Rozier tested the flammability of hydrogen by gulping a mouthful and blowing across an open flame, proving at a stroke that hydrogen is indeed explosively combustible and that eyebrows are not necessarily a permanent feature of one’s face. Cavendish, for his part, conducted experiments in which he subjected himself to graduated jolts of electrical current, diligently noting the increasing levels of agony until he could keep hold of his quill, and sometimes his consciousness, no longer. In the course of a long life Cavendish made a string of signal discoveries—among much else he was the first person to isolate hydrogen and the first to combine hydrogen and oxygen to form water—but almost nothing he did was entirely divorced from strangeness. To the continuing exasperation of his fellow scientists, he often alluded in published work to the results of contingent experiments that he had not told anyone about. In his secretiveness he didn’t merely resemble Newton, but actively exceeded him. His experiments with electrical conductivity were a century ahead of their time, but unfortunately remained undiscovered until that century had passed. Indeed the greater part of what he did wasn’t known until the late nineteenth century when the Cambridge physicist James Clerk Maxwell took on the task of editing Cavendish’s papers, by which time credit had nearly always been given to others. Among much else, and without telling anyone, Cavendish discovered or anticipated the law of the conservation of energy, Ohm’s law, Dalton’s Law of Partial Pressures, Richter’s Law of Reciprocal Proportions, Charles’s Law of Gases, and the principles of electrical conductivity. That’s just some of it. According to the science historian J. G. Crowther, he also foreshadowed “the work of Kelvin and G. H. Darwin on the effect of tidal friction on slowing the rotation of the earth, and Larmor’s discovery, published in 1915, on the effect of local atmospheric cooling . . . the work of Pickering on freezing mixtures, and some of the work of Rooseboom on heterogeneous equilibria.” Finally, he left clues that led directly to the discovery of the group of elements known as the noble gases, some of which are so elusive that the last of them wasn’t found until 1962. But our interest here is in Cavendish’s last known experiment when in the late summer of 1797, at the age of sixty-seven, he turned his attention to the crates of equipment that had been left to him—evidently out of simple scientific respect—by John Michell. When assembled, Michell’s apparatus looked like nothing so much as an eighteenth-century version of a Nautilus weight-training machine. It incorporated weights, counterweights, pendulums, shafts, and torsion wires. At the heart of the machine were two 350-pound lead balls, which were suspended beside two smaller spheres. The idea was to measure the gravitational deflection of the smaller spheres by the larger ones, which would allow the first measurement of the elusive force known as the gravitational constant, and from which the weight (strictly speaking, the mass)5 of the Earth could be deduced. Because gravity holds planets in orbit and makes falling objects land with a bang, we tend to think of it as a powerful force, but it is not really. It is only powerful in a kind of collective sense, when one massive object, like the Sun, holds on to another massive object, like the Earth. At an elemental level gravity is extraordinarily unrobust. Each time you pick up a book from a table or a dime from the floor you effortlessly overcome the combined gravitational exertion of an entire planet. What Cavendish was trying to do was measure gravity at this extremely featherweight level. Delicacy was the key word. Not a whisper of disturbance could be allowed into the room containing the apparatus, so Cavendish took up a position in an adjoining room and made his observations with a telescope aimed through a peephole. The work was incredibly exacting and involved seventeen delicate, interconnected measurements, which together took nearly a year to complete. When at last he had finished his calculations, Cavendish announced that the Earth weighed a little over 13,000,000,000,000,000,000,000 pounds, or six billion trillion metric tons, to use the modern measure. (A metric ton is 1,000 kilograms or 2,205 pounds.) Today, scientists have at their disposal machines so precise they can detect the weight of a single bacterium and so sensitive that readings can be disturbed by someone yawning seventy-five feet away, but they have not significantly improved on Cavendish’s measurements of 1797. The current best estimate for Earth’s weight is 5.9725 billion trillion metric tons, a difference of only about 1 percent from Cavendish’s finding. Interestingly, all of this merely confirmed estimates made by Newton 110 years before Cavendish without any experimental evidence at all. So, by the late eighteenth century scientists knew very precisely the shape and dimensions of the Earth and its distance from the Sun and planets; and now Cavendish, without even leaving home, had given them its weight. So you might think that determining the age of the Earth would be relatively straightforward. After all, the necessary materials were literally at their feet. But no. Human beings would split the atom and invent television, nylon, and instant coffee before they could figure out the age of their own planet.
Thank you very much for the historical presentation. I have trobule with this experiment. Cavendish experiment design is not measuring Earth's density but measuring air density. G published values in past few decades have changed from 6.672 x 10@ -11 to latest value of G = 6.67384 x 10^ -11 is a measurement of air density. To start with you have two meatl balls not in touch with Earth but in touch with air. Newton's equation is F = G mM/(r.r): G uints is 1/d (t.t); d = density and t = time; G = 1/(4pi/3)(2/5)d (t.t); volume factor of air (4pi/3); spherical moment of inertia used in the experiment (2/5); t = sidreal time; d = air density = 1.2041km/(m.m.m)
I took Cavedndish experiment and had it inside a glass chamber and sucked air out and gravity vanished. It is alson very well known that gravity is reduced with altitude where Earth's mass and density is not lower but air density and mass is lower
Quote : "I took Cavedndish experiment and had it inside a glass chamber and sucked air out and gravity vanished" WHAAAAT???? Gravity vanished!?!
oh i would love to chime in here .. but i know my argument would confuse the issue ...as far as the Cavedndish experriment one could argue that the lack of conductive material , the aloted space in the vaccume would allow for the apperance of lack of gravity ( * NOTE * i argure that G is actualy a extencion of EM not a force unto itself ...this is UNPROVEN .... but makes more sence ) and as far as altitude and the weeking effect of gravity ....one could argue that the further you are from a EM pull / effect the weeker it is on the opposing object ......( again * NOTE * this is just my point of view do not try to argue this in class as it WILL be counter productive )
phloyd.. don't put your view here.. lets discuss your gravity view only that other thread you opened :D... lets not confuse the poor chap :D.. but i can prove you you are wrong though!
i put in my disclaimer ( *NOTE *) ...lol
@Realtimephysics. Gravity and air pressure are completely unrelated. If vacuums made gravity disappear then planets wouldn't be held in orbit in space. Gravity and air resistance are both forces, and as such, they can each separately contribute to the motion of a falling object but as for Cavendish, he was measuring two masses, the distance between them, and the force of gravity (technically, the force of the torsion spring at a point when it was in equilibrium with the force of gravity) - with those measurements G is the only unknown left in Newton's law of universal gravitation. He wasn't interacting with the air or the earth, the interaction was strictly between the lead spheres.