∴ Expression for variation of g with latitude, g′=g−Reω2cos2λ ∵Re=R and for equator λ=0°. ∴g′=g−Rω2 Multiply with m on both sides, we get mg′=mg−mRω2 ∵ For weightless, mg′=0 ∴0=mg−mRω2 ∴ Angular speed of Earth, ω=√