Children experience the physical properties of liquids as they watch raindrops run down a window, observe how insects can walk on water, and notice how the “shape” of a liquid matches the container in which it is held. Thinking about similarities and differences among liquids helps to build foundational ideas of matter and molecular structure. In the following lesson, students explore the cohesiveness and surface tension of two liquids. Through observations and interactions, students develop an understanding about how liquids are similar and different.