Torsion spring

A torsion balance (also: torsion ) is used since the 19th century for measuring very small forces, such as gravitational attraction ( gravity ) between two lead balls or the electrostatic attraction between two oppositely charged bodies.

A similar instrument was developed in 1910 by geophysicist L.Eötvös for measuring gravity gradients. It served, inter alia, the exploration of underground resources and the geoid determination.

The principle of operation of the first type of instrument is a large, stationary mass ( lead bullet ) draws a smaller ball to gravitationally. To a rod is centrally suspended from a torsion wire and the ends thereof each have a small mass ball. Two large ground balls are mounted at a suitable distance and symmetrically with respect to the rotatable hanging balls. The mutual attraction then causes a deflection or rotation of the rod which is opposed to the torsion of the wire. From the angle of rotation, the gravitational constant can be calculated.

Most the acting force is so small that the change in position of the ball by the deflection of a light beam through a mirror attached to the suspensor ( light pointer ) must be sufficiently enlarged to be determined accurately. In order not to affect the measurement due to air resistance, the balance is in an evacuated vessel.

With the torsion balance for the first time was for the physics and technology ( eg in space) very important gravitational constant

Determined.

Historical data

The principle of gravitation torsion balance or scale was elaborated for the first time by scientists and used the following:

• 1760 John Michell described the principle of the torsion balance and built a device, then took care, however, to other areas of science.
• 1784 Charles -Augustin de Coulomb, described the use of a torsion balance to study the repulsive and attractive forces of electric charges.
• About 1797 came Michell's apparatus on Francis John Hyde Wollaston in the hands of Henry Cavendish, and these are the forces of attraction of masses measured and thus determined the gravitational constant. In his report to the Royal Society about his experiments Cavendish explicitly pointed to the merits of Michell.
• 1906 built geophysicist Loránd Eötvös a modification of the torsion balance and certain of his hand, the gravitational constant. Therefore, it is often also regarded as the "inventor " of the torsion balance.
• Around 1920 developed Eötvös appropriate for the measurement of gravity gradients torsion balance. With it, the geophysical exploration of oil deposits and in the Great Hungarian Plain and the measurement of deflections of the vertical starts.