- #1

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[tex]\[

{\mathbf{F}} = \frac{{Gm_1 m_2 }}

{{r^2 }}

\]

[/tex]

and Coulomb's law is

[tex]

\[

{\mathbf{F}} = \frac{{Qq_1 q_2 }}

{{r^2 }}

\] [/tex]

We know from comparing the dimensions of the first equation that G, the gravitational constant, has the dimension

[tex]\[

[M^{ - 1} L^3 T^{ - 2} ]

\]

[/tex]

But for Coulomb's law, we assume Q is dimensionless. Why do we make this assumption?