Cavendish Torsion Balance: Measuring Newton's Gravitational…

What is the Cavendish Torsion Balance?

The Cavendish Torsion Balance is a precision instrument designed by British scientist Henry Cavendish to measure the gravitational force between masses. It consists of two small test masses suspended from a thin wire, which is twisted when larger masses are brought close. The balance point reveals the gravitational constant G.

This experiment not only confirmed Newton’s law of universal gravitation but also provided an accurate value for G, crucial in understanding planetary motion and stellar dynamics.

How Does It Work?

When two small masses are suspended by a torsion fiber, they experience a gravitational attraction from nearby larger masses. This attraction causes the fiber to twist slightly until an equilibrium is reached. The angle of twist is proportional to the product of the masses and inversely proportional to the square of their distance apart, according to Newton’s law of gravitation.

By measuring this angle and knowing the physical properties of the torsion fiber (such as its stiffness), one can calculate G.

live demo · related simulation● LIVE

Why is It Important?

The Cavendish Torsion Balance demonstrated that gravitational forces could be measured with high precision, validating Newton’s theory and opening up new avenues in experimental physics.

Today, it serves as a benchmark for modern gravitation experiments and continues to inspire advancements in precision measurements.

Real-World Applications

The principles behind the Cavendish Torsion Balance are used in various fields today. For instance, it forms the basis of gravitational wave detectors like LIGO and Virgo, which require precise measurements to detect minute changes in distance caused by passing gravitational waves.

Additionally, it aids in understanding the distribution of mass within planets and stars, contributing to our knowledge of celestial mechanics.

Frequently asked questions

How did Cavendish ensure accuracy in his measurements?

Cavendish used a highly sensitive torsion balance with a very thin wire that could detect small angular displacements. He also conducted multiple trials and averaged the results to minimize errors.

What are some modern variations of the Cavendish experiment?

Modern versions use laser interferometry for greater sensitivity, such as in the Eöt-Wash experiments which test the equivalence principle by measuring tiny differences in gravitational forces on different materials.

Why is G still considered a fundamental constant if it can be measured?

G is considered fundamental because it appears in many physical equations and its value cannot be derived from other constants. It must be measured experimentally, making the Cavendish Torsion Balance crucial for defining our understanding of gravity.

How has technology improved upon Cavendish’s original apparatus?

Modern instruments use more precise materials and techniques to reduce noise and improve sensitivity. They also incorporate automation and data analysis software to enhance accuracy and reliability.

Try it live

Everything above runs in your browser — open Cavendish Torsion Balance (2D) — Measuring Newton's G and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.

▶ Open Cavendish Torsion Balance (2D) — Measuring Newton's G simulation

Cavendish Torsion Balance: Measuring Newton's Gravitational Constant