Of state. Contents and Concepts 1. Comparison of Gases, Liquids, and Solids Changes of State

FIGURE 11.16

Explaining surface tension

Note that a molecule at the surface experiences a net force toward the interior

of the liquid, whereas a molecule in the interior experiences no net fo

Surface Tension

As Figure 11.16 illustrates, a molecule within the body of a liquid tends to be attracted equally in all directions, so that it experiences no net force. On the other hand, a molecule at the surface of a liquid experiences a net attraction by other molecules toward the interior of the liquid. As a result, there is a tendency for the surface area of a liquid to be reduced as much as possible. This explains why falling raindrops are nearly spherical. (The sphere has the smallest surface area for a given volume of any geometrical shape.)

Energy is needed to reverse the tendency toward reduction of surface area in liquids.