Cavendish torsion scale experiment
Mechanics in Motion · Interactive
- DimensionsSubject to on-site plan
- PresentationInteractive
- PricingQuoted by manufacture spec
Purpose & Scientific Principle
Restore the process of Cavendish torsion scale experiment and introduce Cavendish's method of testing the weight of the earth.
How to Operate
Cavendish installed a small lead ball on each end of a long wooden stick, like a dumbbell, and then used a quartz wire to hang the "dumbbell" horizontally. During the experiment, as long as the two large shot balls are brought close to the small shot balls at both ends of the wooden stick, due to the effect of "gravity", the "dumbbell" will definitely swing and the quartz wire will also twist. As long as you measure how much the quartz wire twists, you can know the gravity between the big and small lead balls.
At the same time, he fixed a small mirror on the quartz wire and illuminated the small mirror with a beam of light. A small mirror reflects light onto a scale. In this way, as long as the quartz wire twists slightly, the reflected light will move significantly on the scale, thus improving the sensitivity of the experiment.
He measured the parameters of the gravitational constant. The gravitational constant is approximately G=6.67259x10-11 (N·m2/kg2). G=6.67×10-11 (N·m2/kg2) is usually taken. On this basis, Cavendish calculated the density and mass of the earth. Cavendish's calculation result is that the mass of the earth is 6.0x1024kg. This result has an error of less than 1% compared with the results measured by modern instruments. Judging from the experimental conditions at the time, it was quite an achievement.
The formula of universal gravitation F=Gm1m2/r2 (G is the gravitational constant, m1 and m2 are the masses of the two objects, and r is the distance between the two objects). But Newton himself did not know what the value of the gravitational constant G was. It was not until 1798 that Cavendish verified the law of universal gravitation through the torsion balance experiment and determined the gravitational constant and the average density of the earth. He is known as "the first person to weigh the earth." The exhibit describes Cavendish's experimental process in the form of scene restoration.
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