Official websites use .gov A .gov website belongs to an official government organization in the United States. Secure .gov websites use HTTPS A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites. National Park Service Search Exiting nps.gov Rate the Lesson Plan Student Activities Sand Density Grade Level: Upper Elementary: Third Grade through Fifth Grade Subject: Science This activity, which uses sand, helps students will understand material density as it relates to water and sedimentary rocks. Sedimentary rocks