![]() It is surprisingly accurate, about 1% above the modern value (comparable to the claimed standard uncertainty of 0.6%). ![]() In spite of the experimental design being due to Michell, the experiment is now known as the Cavendish experiment for its first successful execution by Cavendish.Ĭavendish's stated aim was the "weighing of Earth", that is, determining the average density of Earth and the Earth's mass. Their faint attraction to other balls placed alongside the beam was detectable by the deflection it caused. He used a horizontal torsion beam with lead balls whose inertia (in relation to the torsion constant) he could tell by timing the beam's oscillation. He determined a value for G implicitly, using a torsion balance invented by the geologist Rev. The first direct measurement of gravitational attraction between two bodies in the laboratory was performed in 1798, seventy-one years after Newton's death, by Henry Cavendish. G M = 3 π V P 2, īased on this, Hutton's 1778 result is equivalent to G ≈ 8 ×10 −11 m 3⋅kg −1⋅s −2.ĭiagram of torsion balance used in the Cavendish experiment performed by Henry Cavendish in 1798, to measure G, with the help of a pulley, large balls hung from a frame were rotated into position next to the small balls. Definition Īccording to Newton's law of universal gravitation, the magnitude of the attractive force ( F) between two bodies each with a spherically symmetric density distribution is directly proportional to the product of their masses, m 1 and m 2, and inversely proportional to the square of the distance, r, directed along the line connecting their centres of mass: The first implicit measurement with an accuracy within about 1% is attributed to Henry Cavendish in a 1798 experiment. The modern notation of Newton's law involving G was introduced in the 1890s by C. In SI units, its value is approximately 6.674 ×10 −11 N⋅m 2/kg 2. ![]() The measured value of the constant is known with some certainty to four significant digits. In the Einstein field equations, it quantifies the relation between the geometry of spacetime and the energy–momentum tensor (also referred to as the stress–energy tensor). In Newton's law, it is the proportionality constant connecting the gravitational force between two bodies with the product of their masses and the inverse square of their distance. The gravitational constant (also known as the universal gravitational constant, the Newtonian constant of gravitation, or the Cavendish gravitational constant), denoted by the capital letter G, is an empirical physical constant involved in the calculation of gravitational effects in Sir Isaac Newton's law of universal gravitation and in Albert Einstein's theory of general relativity. The gravitational constant G is a key quantity in Newton's law of universal gravitation. Not to be confused with g, the gravity of Earth.
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