Gravitational Constant — Definition

Definition

Imagine you have two objects, say two apples, and you want to know how strongly they pull on each other due to gravity. Newton's Law of Universal Gravitation tells us that there's a force of attraction between any two objects with mass.

This force depends on how heavy each object is (their masses) and how far apart they are. But there's also a 'magic number' that ties it all together, making the equation work and giving us the actual strength of this pull.

That 'magic number' is the Universal Gravitational Constant, represented by the capital letter $G$.

Think of $G$ as the 'gravitational strength factor' of the universe. It's a constant because its value doesn't change, no matter where you are in the universe, what objects you're looking at, or what's between them. It's not like the acceleration due to gravity on Earth, $g$, which changes depending on your altitude or location. $G$ is truly universal.

Its value is incredibly small, approximately $6.674 \times 10^{-11}$ Newton-meter squared per kilogram squared ($N cdot m^2/kg^2$). This tiny value explains why we don't feel the gravitational pull between everyday objects like two people or two cars.

The masses of these objects are simply too small for their mutual gravitational force to be noticeable. However, when you deal with massive objects like planets, stars, or galaxies, their enormous masses multiply this tiny $G$ value enough to create the immense gravitational forces that shape the cosmos, holding planets in orbit around stars and stars within galaxies.

So, in essence, $G$ is the fundamental constant that dictates the strength of gravity. It's a scalar quantity, meaning it only has a magnitude and no direction. It's crucial for understanding everything from how an apple falls to how galaxies interact, serving as a cornerstone of classical physics.