Which scientific phenomenon is best suited as an anchor for a second-grade unit on the structure and properties of matter?

The chosen phenomenon about an ice cube melting in a glass and then becoming solid again when the water is frozen is an excellent anchor for a second-grade unit on the structure and properties of matter. This example clearly illustrates the concepts of states of matter—solid, liquid, and back to solid—making it tangible for students to observe and understand. It involves a familiar experience, as children often encounter ice and water in their daily lives, which helps make the learning relevant and engaging.

Furthermore, this phenomenon allows for hands-on learning opportunities. Students can engage in experiments to observe melting and freezing, providing a visual representation of how matter changes with temperature. The phase changes can easily be linked to discussions about the properties of solids and liquids, reinforcing key scientific concepts in a way that is accessible and understandable for young learners.

In contrast, while the other options present interesting observations, they aren't as encompassing when it comes to teaching the fundamental concepts of matter. For example, shadows and their temperature differences do not directly address the physical states of matter or their properties. Similarly, the static electricity phenomenon with the balloon provides a glimpse into molecular interactions but may not comprehensively cover the complete scope of matter's structure. Burning a match demonstrates a chemical change rather than focusing on physical changes