The well known theorems of Khintchine and Jarník in metric Diophantine approximation provide a comprehensive description of the measure theoretic properties of real numbers approximable by rational numbers with a given error. Various generalisations of these fundamental results have been obtained for other settings, in particular, for curves and more generally manifolds. In this paper we develop the theory for planar curves by completing the theory in the case of parabola. This represents the first comprehensive study of its kind in the theory of Diophantine approximation on manifolds.1.1. Dual Diophantine approximation. To set the scene for the problems considered in this paper, we first recall the fundamental results in the theory of dual Diophantine approximation. Let ψ : R + → R + denote a real positive decreasing function. We refer to ψ as an approximating function. Define the set W (ψ) := x = (x 1 , . . . , x n ) ∈ R n : |a 0 + a 1 x 1 + · · · + a n x n | < ψ(|a|)where 'i.m.' stands for 'infinitely many' and |a| = max{|a 1 |, . . . , |a n |} is the standard supremum norm. A vector x ∈ W (ψ) will be called ψ−approximable. In the case ψ(r) = r −τ for some τ > 0 we also say that x is τ −approximable and denote W (ψ) by W (τ ). The first significant result in the theory is Dirichlet's theorem which tells us that W (n) = R n .The following fundamental result provides a beautiful criterion for the 'size' of the set W (ψ) in terms of n-dimensional Lebesgue measure | · | n .