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So when mg is < than the resultant force, mg is acting downward but there is a greater force than this toward the centre, so to compensate for this the contact force must also be acting downward, so F=mg+R ( where R is the contact force ).

And when mg is > than the resulstant force, the contact force must be acting upward to provide the smaller centripetal force, so F= mg -R.

But at the bottom F always = R-mg.

*However I am confused with vertical circles where e.g. a stone is being whirled. The formula for the top of the circle is always given as F = T + mg, where T is the tension. So T always acts downwards? I don't really understand this...thanks !*