2. For manufacturing waterproof (non-wetting) umbrella, a fabric and a chemical will be paired. There are two alternatives for both fabrics (N and L) and chemicals (S and T). The surface tension characteristics between phases air, rain droplet and the fabrics after treatment with the chemicals are given as mN/m in the tables below: Chemicals Chemicals S T S T Surface tension between air and fabric, YFA N Fabrics L Surface tension between droplet and fabric, 1 FD N Fabrics L 44 32 18 10 20 32 42 45 a) Write the force balance among fabric (F), air (A), and rain droplet (D) on the horizontal plane, after drawing a rain droplet on the fabric and indicating the three forces on it. b) Calculate the contact angles for all fabric-chemical pairs (NS, NT, LS, LT). c) Which fabric-chemical pair do you recommend for this purpose, if the surface tension between rain droplet and air ypa is 70 mN/m