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Pendulum Experiments

The pendulum has played a particularly key role in physics, in conjunction with the evolving theories of planetary orbit and gravitation. Indeed, many famous scientists, including Galileo, have made breakthrough discoveries by observing pendulums. A pendulum consists of an object, usually a metal disc, attached to a chain and hanging from a fixed point that, when drawn back and then released, swings freely in a downward arc by the force of gravity alone, and then swings in an upward arc when it reaches its mid-point because of inertia.

Experimental Observations Using Pendulums
- If a pendulum were placed in a frictionless vacuum it could continue to swing forever, but otherwise it would eventually slow and stop due to air resistance. As a result of its ability to move subject almost exclusively to gravity, the pendulum has long been used as a device for time keeping, although it has since been replaced by more accurate atomic clocks. Its ability to simulate the effects of gravity has meant that it has played an extensive role in the science of geodesy.
Galileo's Pendulum Experiments
- It is said that Galileo first observed a pendulum's motion when he observed the swinging bronze chandelier in the cathedral of Pisa, in Italy, and apparently used his own pulse as a timer. The famous astronomer conducted a number of experiments with pendulums, and from observing the devices' movement, asserted that the swing of a simple pendulum is isochronus---meaning that the pendulum swings from side to side with equal time intervals---provided the length remains the same. This is regardless of how large its arc or amplitude is. He also observed that the square of the period of the pendulum's swing, which is the time taken for the pendulum to make one full swing, varies directly with the length of its chain.
Benjamin Robins' Ballistic Pendulum Experiment
- Benjamin Robins, a British mathematician and engineer, devised a pendulum experiment to measure the velocity of projectiles and published his work in "Principles of Gunnery," released in 1742. To measure the velocity of a bullet, he fired a gun at a pendulum disc made of wood. As the pendulum moved, it pulled a ribbon through a slot in the pendulum's mounting, and the length of ribbon pulled through is equal to the length of the pendulum's swinging arc. Robins used the length of the swing arc to calculate the vertical distance through which the pendulum moved, and thus arrive at the bullet's change in gravitational potential energy.
Edward Sabine's Pendulum Experiments
- Edward Sabine was a British scientist and soldier who made important experimental observations using a pendulum regarding the Earth's globular shape. Sabine was a member of John Ross's expedition in 1818 to discover the Northwest Passage. On the route he conducted experiments using a pendulum during his trip and he noted down variations that he observed in the period of vibrations of the pendulum at different latitudes. This information provided evidence of the Earth's magnetic field and its globular shape.

Astronomy