We explain “G”, the gravitational constant discovered by Isaac Newton.
Isaac Newton revolutionized the field of physics, when in 1687 he published “Philosophiae naturalis principia mathematica” , also known as “Principia” .
In this publication, Newton established the foundations of classical mechanics through his laws, found and verified through experimentation.
In this article we will explain to you one of the concepts that Newton gave rise to and that is still somewhat mysterious to this day: “G”, or the universal gravitational constant.
What is gravity?
We all know the famous story according to which Isaac Newton realizes the existence of gravity after an accident under an apple tree, in which an apple fell on his head . According to Newton himself, this phenomenon revealed to him that a force was pulling the apple toward the earth, which he would end up proving by postulating his calculations for gravity in his Principia De Him.
Gravity is a fundamental force in the universe, according to which everything that has mass exerts an attraction on other objects . This attraction occurs between planets and stars, toast and the ground, or any system you can think of, as long as they have mass.
Isaac Newton defined the equation that allowed calculating the gravitational force between two objects as the masses of the attracting objects divided by the distance between them squared, multiplied by a constant that he named “G” .
When we talk about objects of similar size, this equation is used. But the Earth’s gravitational force on its surface is known, an acceleration value of 9.8 m/s on all objects on it. When we talk about masses as disparate as those of a planet on a human being or an apple, the masses of the latter are practically negligible due to their smallness.
Hence, despite having different masses and, furthermore, that the gravitational equation depends on the mass of both objects, the force of Earth’s gravity remains relatively similar regardless of the object we are checking.
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What is G?
G had a value that Newton did not know, since he did not know the mass of the planet earth either . It was called the universal gravitational constant, and Newton knew it had to be of an incredibly small value, since gravitational effects between everyday objects are not observed on a day-to-day basis.
Newton was right about the characteristics of G, but it wasn’t until 1798 that the amazing natural philosopher (revolutionary chemist and physicist at the time) Henry Cavendish experimentally calculated the value of G , using an experimental model from another amazing physicist of the time friend yours, John Mitchell.
As a curiosity we could mention that John Mitchell was also ahead of his time, postulating the possible existence of black holes, a method of manufacturing artificial magnets or that earthquakes traveled in waves. The only known details of Mitchell’s physique are that he was a short, fat man with a black complexion.
After John Mitchell’s death, Henry Cavendish continued one of the experiments he bequeathed to him. A way to measure the gravitational force between two objects , by means of a system of isolated elements in suspension. In this way Henry Cavendish managed to calculate the universal gravitational constant, G.
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How much is G worth?
Currently the value of G is accepted as 6.66704810 x 10^-11 , an incredibly small value that agrees with Newton’s estimates. Cavendish’s experiments managed to get close to this value, with an estimate that was 1% wrong with respect to our current knowledge.
The value of G is disputed even today, despite being used in very important physical equations. This is due to a number of reasons, such as:
1. Gravity affects all objects with mass
It is difficult to measure gravity since the measuring devices we use will have mass and will have an effect on the experiment. The number of factors to consider to accurately calculate the force of attraction between real objects is very daunting , since any object can influence the system we are measuring.
2. We cannot derive G from other constants
There are many constants and values used in science that are inferred rather than measured. Unfortunately this is not the case with the universal gravitational constant, which today needs to be measured experimentally.
Currently, despite the fact that we use a specific value of G, we know that this value is not necessarily the correct one, but rather the best estimate that we have been able to obtain from a range of values that is too wide .
Is the universal gravitational constant useful?
Of course. The universal gravitational constant is a value that we can use in multiple formulas with different applications. Thanks to our estimates of G, we can know the gravitational force that the planets exert on the objects on their surface .
Furthermore, the universal gravitational constant appears in Max Plank’s equations in which he determined the shortest possible distance in the universe (the Plank distance) as well as the shortest possible time interval (the Plank time).
Science should not act dogmatically, as if everything that has been said in the past is true. People like Newton, capable of changing our paradigms, remind us that we have to remain humble about the explanations we give to the universe , since there may be unknown factors that lead us to other conclusions.
The universal gravitational constant is no exception. With values constantly revised to be able to define it more and more precisely, it is constantly used despite the fact that we do not know the reason for its value or its exact value.
The most important thing in these cases is to recognize that we do not have all the information, but we can move forward knowing that there are gaps in our knowledge. Whether these holes matter or not, we’ll know once they’re cleared up .
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.