When the molecules near the liquid surface move outward from the equilibrium position, the external air and vapor molecules have little repulsive force on it. Did not play an important role. It is only attracted by internal molecules, so the force to restore it to its equilibrium position is not as great as that in liquid, which makes the vibration amplitude of surface molecules larger than that in liquid, and some molecules with large kinetic energy may rush out of the suction range and become vapor molecules, resulting in the sparse distribution of molecules on the surface than in liquid, and the distance between molecules is relatively large (r >: R0), precisely because of the sparse distribution of molecules inside the liquid surface and the molecular spacing r >; R0, intermolecular attraction prevails, leading to surface tension of liquid. Therefore, the essence of liquid surface tension is the resultant force of intermolecular interaction, which points to the inside of the liquid. It can be seen that the force that holds up the coin cannot be the surface tension of the liquid. Then let's look at buoyancy again.