Toppling speed on level rails
= Toppling speed on level rails
{title2=$v_0=\sqrt{gRd/(2h)}$}
A vehicle with <centre of mass> midway between level rails separated by d, at height h, follows a turn of <radius> R. Vertical <force> balance and cross-sectional <moment balance> give inner rail reaction $mg/2-mv^2h/(Rd)$. Its first zero occurs at the displayed speed. This is a toppling criterion under maintained lateral contact, not a guarantee against sliding or suspension instability.