Inertial mass
= Inertial mass
{title2=$m_{\rm i}$}
In <Newtonian mechanics>, inertial <mass> is the coefficient in $\mathbf F=m_{\rm i}\mathbf a$, measuring a body's response to a net <force>. The <weak equivalence principle> makes its ratio to passive <gravitational mass> universal; choosing compatible units then sets the two equal.