What is Surface Tension? This Cool Video from Space Helps

Any action or movement in the world is the result of a lot of push-and-pull by various forces, many of which may be invisible to us. For example, when we wring a wet wash cloth, our muscles’ force will squeeze first the air molecules and then water out of the cloth fibers. But water molecules will only move if the compression force is greater than their adhesive force to cloth’s fiber surfaces. Even then, the portion of dislodged water droplets that get to the outer surface of the wrought cloth would only drop if the force of gravity on them is greater than surface tension — the cohesive force holding surface molecules together. That is why regardless of how hard we squeeze a wash cloth, we still have some water left in the cloth and some on the cloth. Water is known to have one of the strongest surface tensions among all liquids (fluids), maybe because life depends on it! Only mercury, a liquid metal, has a higher surface tension (about seven times higher) than of water. That is why mercury does not easily stick to other surfaces and mercury molecules usually like to stick together.

But force fields are different in space where gravity is low. This interesting video from 2013 shows how surface tension of water molecules holds them together before and after wetting a wash cloth in the microgravity of the Earth-orbiting International Space Station.