Due to rotation of earth, g‌eff ‌=g−ω2Rcos2θ Where ' θ ' is angle made with equator Also, At poles, θ=90∘ ‌∆g=ω2Rcos2θ ‌‌‌=ω2Rcos290=0 [no effect on poles] g‌eff ‌=g−ω2Rcos2θ for equator θ=0∘ So, g‌eff ‌=g−w2R ∆g=ω2R (Which is maximum change)