Assume the temperature function to vary linearly over the length of a bar as T = t1 + t2 x; that is, express the temperature function as {T} = [N] {t}, where [N] is the shape function matrix for the two-node bar element. In other words, [N] = [1 - x/L x/L]. Determine the force matrix in terms of E, A, α, L, t1, and t2.