Finding G
Dr. Beams also applied his knowledge of rotating systems to the
measurement of G, the universal constant of gravitation. G was first
measured by Henry Cavendish in 1798. Cavendish used a torsion balance
to measure the force with which a small lead ball was attracted to a
larger ball. In Beams' experiment a cavendish balance is mounted on a
table that can rotate about the vertical axis. As the two large
masses begin to twist a torsion pendulum, a servomechanism begins to
rotate the table at exactly the rate eneded to keep the torsion
pendulum from ever getting any nearer the large masses. Throughout
each experimental run the rotary table is continuously accelerated;
the values of the required acceleration can be used to compute G. The
fact that the entire system is rotating tends to cancel out the
effects of nearby massive objects on the experiments. Dr. Beams' 1969
experiment was the first substantial change in the method of measuring
G since 1942.
Dr. Beams also applied his knowledge of rotating systems to the
measurement of G, the universal constant of gravitation. G was first
measured by Henry Cavendish in 1798. Cavendish used a torsion balance
to measure the force with which a small lead ball was attracted to a
larger ball. In Beams' experiment a cavendish balance is mounted on a
table that can rotate about the vertical axis. As the two large
masses begin to twist a torsion pendulum, a servomechanism begins to
rotate the table at exactly the rate eneded to keep the torsion
pendulum from ever getting any nearer the large masses. Throughout
each experimental run the rotary table is continuously accelerated;
the values of the required acceleration can be used to compute G. The
fact that the entire system is rotating tends to cancel out the
effects of nearby massive objects on the experiments. Dr. Beams' 1969
experiment was the first substantial change in the method of measuring
G since 1942.