# Definition:Gravitational Constant

## Physical Constant

The constant of proportion $G$ in Newton's Law of Universal Gravitation is a physical constant.

Its value in SI units is referred to as $G$ and is approximately equal to $6.674 \times 10^{-11} \, \mathrm N \, \mathrm m^2 \, \mathrm{kg}^{-2}$.

## Dimensional Analysis

Using the techniques of dimensional analysis, we see that $G$ has dimension $M^{-1} L^3 T^{-2}$.

## Also see

**Gravitational Constant: $G = 6.67 \times 10^{-8} \, \mathrm{cm}^{-3} \, \mathrm{gm}^{-1} \, \mathrm{sec}^{-2}$** is a track by Type O Negative on their 1991 album Slow, Deep and Hard. It is about committing suicide.

As well it might be. If I'd had to express the physical constants in CGS units when I'd been in college, I doubt I'd have found a reason to stay alive myself.

## Historical Note

When Isaac Newton formulated his Law of Universal Gravitation, he did not know, and had no immediate means to determine, what the gravitational constant $G$ actually is.

The value of $G$ was determined in $1789$ by Henry Cavendish in what is now known as the Cavendish experiment.

## Sources

- 1966: Isaac Asimov:
*Understanding Physics*: $\text{I}$: Chapter $4$ - 1972: George F. Simmons:
*Differential Equations*... (previous) ... (next): $\S 3.21$: Newton's Law of Gravitation - 1992: George F. Simmons:
*Calculus Gems*... (previous) ... (next): Chapter $\text {B}.25$: Kepler's Laws and Newton's Law of Gravitation