SafekipediaThe gravitational constant is an empirical physical constant that tells us how strong the pull of gravity is between any two objects with mass. It helps scientists calculate how much gravitational force exists between objects, whether they are planets, stars, or everyday items. This constant is very important in understanding both Sir Isaac Newton's ideas about gravity and Albert Einstein's more advanced theory of general relativity.
In Newton’s version of gravity, the gravitational constant connects the force of gravity between two objects to their masses and how far apart they are. In Einstein’s work, it helps explain how the shape of space and time changes because of mass and energy.
Scientists have measured the gravitational constant fairly accurately, and in the standard units we use today, its value is about 6.6743×10−11 m3⋅kg−1⋅s−2. This means it is a very small number, showing that gravity is a relatively weak force compared to other forces in the universe. The constant was first measured carefully by Henry Cavendish in a famous 1798 experiment, and its symbol today is the capital letter G.
Definition
The gravitational constant shows how strong the pull of gravity is between two objects. According to Sir Isaac Newton, the force of gravity between two objects depends on their masses and the distance between them. The bigger the objects and the closer they are, the stronger the gravitational pull. This constant, usually called "Big G," helps us calculate this force.
In Albert Einstein's theory of general relativity, the gravitational constant also plays an important role. It helps describe how mass and energy shape the space around us, influencing how objects move. This constant connects the simple ideas of Newton’s gravity with the more complex ideas of Einstein’s theory.
Meaning
The gravitational constant, denoted by the capital letter G, helps us understand how strong gravity is in the universe. It is measured in units of m3 kg−1 s−2. One way to think about it is that it tells us how much force there is between two objects depending on their mass and how far apart they are. Another way is to see it as how much a mass can pull on something at a distance, causing it to speed up or accelerate.
Value and uncertainty
The gravitational constant is a number that helps scientists understand how strong gravity is. It is hard to measure very precisely because gravity is a very weak force compared to other forces in the universe.
In SI units, which are the standard units scientists use, the CODATA-recommended value of the gravitational constant is:
G = 6.67430(15)×10−11 m3⋅kg−1⋅s−2
This means scientists know the value of G very well, but there is still a tiny bit of uncertainty in the measurement.
History of measurement
Further information: Earth mass, Schiehallion experiment, and Cavendish experiment
The idea of a gravitational constant comes from Newton's law of universal gravitation, which explains how objects attract each other through gravity. Newton suggested that measuring gravity might be possible by looking at how a pendulum swings near a big hill, but he thought the effect would be too small to notice.
The first successful measurement of Earth's density—and indirectly, the gravitational constant—was made in 1776 during the Schiehallion experiment. This helped scientists estimate the masses of the Sun, Moon, and planets. In 1798, Henry Cavendish conducted the Cavendish experiment, using a special tool called a torsion balance to measure the gravitational attraction between lead balls. His results were very close to what scientists use today.
Since then, measuring the gravitational constant has been challenging because gravity is a very weak force. Many scientists have tried to measure it more accurately over the years, but results have varied. Today, scientists continue to work on measuring it more precisely, with recent efforts coordinated by the National Institute of Standards and Technology.
| Year | G [10−11 m3⋅kg−1⋅s−2] | Relative standard uncertainty |
|---|---|---|
| 1969 | 6.6732(31) | 460 ppm |
| 1973 | 6.6720(49) | 730 ppm |
| 1986 | 6.67449(81) | 120 ppm |
| 1998 | 6.673(10) | 1500 ppm |
| 2002 | 6.6742(10) | 150 ppm |
| 2006 | 6.67428(67) | 100 ppm |
| 2010 | 6.67384(80) | 120 ppm |
| 2014 | 6.67408(31) | 46 ppm |
| 2018 | 6.67430(15) | 22 ppm |
| 2022 | 6.67430(15) | 22 ppm |
Constancy
Further information: Time-variation of fundamental constants
Studies of very bright stars called type Ia supernovae suggest that the gravitational constant has stayed almost the same over a very long time. Over the last nine billion years, it has changed by less than one part in ten billion each year. This shows how stable this important science number is.
This article is a child-friendly adaptation of the Wikipedia article on Gravitational constant, available under CC BY-SA 4.0.
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