The sap in trees, which consists mainly of water in summer, rises in a system of capillaries of radius r = 2.5 × 10-5 m. The surface tension of sap is T = 7.28 × 10-2 N/m and the angle of contact is 0o. Does surface tension alone account for the supply of water to the top of all tress?
The height to which the sap will rise is h=ρgr2Tcos0o = 103×9.8×2.5×10−52×7.28×10−2 = 0.6m This is the maximum height to which the sap can rise due to surface tension. Since many trees have heights much more than this, capillary action alone cannot account for the rise of water in all trees.
