How does the droplet of water stay together? Why doesn't it spread out and flow over the edges of the penny? Water is made up of many tiny molecules. These molecules pull on each other, or exert a force. As shown in Figure 2, a water molecule in the middle of a droplet gets pulled equally in all directions by the neighboring molecules. However, a molecule at the surface of the droplet gets pulled mostly inward by the molecules below it. This means that all the molecules at the surface help "hold together" the droplet of water, and this is called surface tension.