R is the radius of the earth and ω is its angular velocity and gp is the value of g at the poles. The effective value of g at the latitude λ=60° will be equal to
gp−14Rω2
gp−34Rω2
gp−Rω2
gp+14Rω2
g=gp−Rω2cos2λ=gp−ω2Rcos260°=gp−ω2R122=gp−14Rω2∵cos60°=12