Cavendish

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Cavendish and the Value of G
The law of universal gravitation states that the gravitational attraction amongst two objects is directly proportionate to their masses times each other and inversely proportional to the distance between the centers squared. This law looks like:

In this very equation, G represents the universal gravitation constant. This constant was not set in stone until Lord Henry Cavendish came across and experimentally determined the value of G using a torsion balance. Cavendish’s device included a light and a stick about 24 inches long. At the ends of the stick, small lead spheres were attached, and the stick was hung by a thin cable. When the stick rotates, the torsion of the cable starts to display a torsional force that is proportionate to the direction or angle of rotation of the stick. The more the cable turns, the more the system reverses back towards its original site. The instrument shown below determines the correlation between the angle of rotation and its torsional force.

Afterwards, Cavendish attached two larger lead spheres near the smaller ones. Because the masses of the objects attract, the large spheres exerted a gravitational force upon the smaller spheres, causing the stick to move slightly. And when the torsional force and the gravitational force came to a balance, Cavendish was able to calculate the gravitational force of attraction between the masses. By computing the mass of the two objects, the distance from the center, and gravitational force the value of G was determined. His calculations resulted in the value of 6.75 x 10-11 N m2/kg2. Today, this value is accepted as 6.67259 x 10-11 N m2/kg2. Because this value is extremely small the force of gravitational attraction favors objects that have large masses. Bibliography

"Cavendish and the Value of G." Cavendish and the Value of G. N.p., n.d. Web. 03 Dec. 2012. <http://www.physicsclassroom.com/Class/circles/U6L3d.cfm>.
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