# Mineral Density

Abstract
Density is a fundamental quality of matter, and a firm understanding of this concept is crucially important to many content areas from earth science to physics, but also provides a framework for the comprehension of mathematical concepts like inverse proportions. Despite this, many students continue to struggle with the relationship between mass, volume, and density, becoming cognitively trapped in misconceptions. Often students will continue to believe that heavy objects are inherently dense, or that heavy objects will sink in water, even after repeated lessons involving the formula for density. Seeing firsthand how this relationship plays out with different objects of various masses and volumes allows students the opportunity to discover the reasoning, and support it with evidence, behind why these misconceptions are false. This plan, aided by the PhET Simulations, allows teachers to fit hours’ worth of density explorations into one 55 minute lesson, avoiding needless mess and safety concerns, and giving students the guided freedom they need to defeat density misconceptions.

Standards

Content Area: Science

Standard: 1. Physical Science

3. Apply an understanding of atomic and molecular structure to explain the properties of matter, and predict outcomes of chemical and nuclear reactions

Inquiry Question 2: Which properties are the most useful in trying to separate mixtures of substances?

Objective
After a previous lesson and a brief review of density, seventh grade students will individually explore the PhET Density Simulator, and then, in small groups, measure the volume and mass, and calculate the density of three mineral samples to within a twenty percent accuracy.

Learning Goals
Students will be able to:
• Explain the relationship between volume, mass, and density
• Describe how changes to either volume or mass affect density

Learning Plan
Critical Question:What is the relationship between volume, mass, and density?
Engage: 5 minutes
Begin by reviewing with the students the various characteristics of minerals we use for categorization. Review how one measures mass and volume, and what density is and how it is found.
Explore: 15 minutes
Allow the students to work through the simulation, seeing for themselves how the densities of the various blocks play out. Encourage them to play with the mystery setting and rank the blocks by density. Ask them how they will find the volumes for the blocks (displacement).
Explain: 10 minutes
Discuss the results of the mystery blocks with the class. If you change the mass of a block and keep the volume the same, what happens to the density? What would one have to do to keep the density from changing? Can you tell what the density of a block will be by looking at the volume of the block? Or just the weight?
Explore (Again): 20 minutes
Have the students work through the measuring and calculating of the mineral densities in small groups or pairs. When each group is finished have them compare results with other groups.
Elaborate: 5 minutes
Bring it back to the critical question. See if the students can describe the relationship. Is density a quality that will change for a mineral over time, or is it consistent? Would we expect every sample of a given mineral to have the same density?
Evaluate:
Students able to calculate mineral densities accurate to within 20 percent of true values will be considered to have successfully met the objective.