« Last post by vhfpmr on Today at 13:20:45 »
I've assumed a spherical earth because I'm arguing about the effect of rotation on a plumb line, not variations in gravity or the effect of rotation on the shape of the earth. If the earth is spherical, 'points at the centre' is the same as 'perpendicular to the surface'.The plumb line only hangs vertically at the equator,For a particular definition of vertical. (essentially: "points to the middle of the Earth").
But if your definition is "perpendicular to the surface of the Earth" then the plumb line is always vertical.
This definition also means that things fall vertically and you can build a vertical tower of bricks without needing cement.Er, no it doesn't. Gravity (G, in black) acts perpendicular to the earths surfaceYou have assumed a spherical Earth- often a reasonable start, but not in this thread about the Earth not being a sphere.