 # What is Density?

#### BOP Curriculum

bop-curriculum@nyharbor.org
Sep 8, 2016

Unit

6-8th

Class Periods

3

Setting

Classroom

Subject Areas

Math

## Summary

Students will compare various substances and discuss the difference between mass and volume. This will lead them to a discussion of density. The class will then jigsaw and each group will find the density of one substance. Then, the teacher will do a demo in which she creates a density column, and the class can see how liquids of different densities behave.

## Objectives

• ﻿What is density?

• How can the same ‘amount’ (volume) of a substance feel heavier?

## Materials and Resources

### Supplies

• 1 large graduated cylinder (100 mL) (for the class)
• 5 10 mL graduated cylinder
• ethanol dishwashing detergent (any brand, but should be colored, e.g. Dawn lemon)
• Dark corn syrup
• vegetable oil
• water
• 4 50 mL cylinders, two full of molasses and two full of alcohol (enough for the whole class to pass around, so you might want to make 3 of each)

## Before you get started

### Tips for Teachers

Note for vocabulary: It is worth discussing with your students the difference between precise scientific terms and imprecise vernacular terms when discussing quantity. In particular contexts, think about: what do you mean when you say "amount" or "quantity"? Are you actually thinking of number? Volume? Mass? Something else? This lesson is structured as a jigsaw. Each group will compute the density of one substance and then the teacher will create the density column for the whole class. The reason for this is that it is very difficult for students to create a density column. If you get any materials on the side of the cylinder, the column will not look good. Make sure to practice the density column in advance. It helps to use a funnel to pour the substances in. Make sure the water is colored so that you can see that it is a different substance. For example, if your dish detergent is yellow, use blue for the water. In this lesson, we use the ideas of weight and mass interchangeably. Make sure students are clear on the difference before plunging in.

N/A

### Background

﻿This lab introduces them to the idea that certain substances are denser than others. Density is a characteristic property of a substance. The density of a substance is the relationship between the mass of the substance and how much space it takes up (volume). The mass of atoms, their size, and how they are arranged determine the density of a substance. The concept of density is essential to understanding how oysters filter. This lesson introduces density.

## Instruction Plan

### Engage

﻿Pass out graduated cylinders that hold 50 mL of molasses and 50 mL of alcohol. The graduated cylinders must be the same size. First, ask what they know about molasses and alcohol? Ask if they're each some kind of water and/or contain water?

### Explore

﻿Divide your class into five groups. Give each group 10 mL of one of the following substances and a scale.

1. ethanol

2. dishwashing detergent

3. dark corn syrup

4. vegetable oil

5. Water (colored blue)

Make sure to write the mass of the graduated cylinder on the board so that the students can subtract that from their total mass.

### Explain

﻿Introduce the formula for density. Explain that density is mass over volume (or how “heavy” something is divided by the space it takes up. In other words, how compact a substance is).  This is a good time to give different examples of the uses of "amount" "more" and "less". Ask students how two objects that are more dense and less dense would feel. What is the difference?

Also, be sure to distinguish between volume and mass/weight!

Use the density calculation handout to have each group find the density of their substance.

### Elaborate

﻿Before beginning this section, have a discussion with students. Ask them to describe things that they think are very dense, and things they think are very rarified (opposite of dense). Then they can make hypotheses about the given substances. Write the name of every substance on the board. Ask for student hypotheses about the density rankings. Once students have proposed different hypotheses and explained their thought processes, rank the substances by the actual densities calculated by the students. Then, collect the samples and pour them into a large graduated cylinder with the most dense on the bottom (see picture on the next page). Now have a discussion about what they see, how it compares to their prediction, and what new insights and questions have come up.

﻿

## Standards

### CCLS - ELA Science & Technical Subjects

• Integrate information presented in different media or formats (e.g., visually, quantitatively) as well as in words to develop a coherent understanding of a topic or issue.

### CCLS - Mathematics

• Reporting the number of observations.

### NGSS - Cross-Cutting Concepts

• #### Patterns

• Graphs, charts, and images can be used to identify patterns in data.
• #### Scientific Knowledge Assumes an Order and Consistency in Natural Systems

• Science assumes that objects and events in natural systems occur in consistent patterns that are understandable through measurement and observation.

### NGSS - Disciplinary Core Ideas

• #### PS1.A: Structure and Properties of Matter

• Each pure substance has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it.

### NGSS - Science and Engineering Practices

• #### Analyzing and Interpreting Data

• Analyze and interpret data to provide evidence for phenomena.
• #### Constructing Explanations and Designing Solutions

• Apply scientific ideas to construct an explanation for real-world phenomena, examples, or events.

### NYC Science Scope & Sequence - Units

• #### Grade 7, Unit 2

• Energy and Matter

### NYS Science Standards - Key Ideas

• #### PS Key Idea 3

• Matter is made up of particles whose properties determine the observable characteristics of matter and its reactivity

### NYS Science Standards - Major Understandings

• Substances have characteristic properties. Some of these properties include color, odor, phase at room temperature, density, solubility, heat and electrical conductivity, hardness, and boiling and freezing points.
• Density can be described as the amount of matter that is in a given amount of space. If two objects have equal volume, but one has more mass, the one with more mass is denser.

### NYS Science Standards - MST

• Students will use mathematical analysis, scientific inquiry, and engineering design, as appropriate, to pose questions, seek answers, and develop solutions.
• Students will understand mathematics and become mathematically confident by communicating and reasoning mathematically, by applying mathematics in real-world settings, and by solving problems through the integrated study of number systems, geometry, algebra, data analysis, probability, and trigonometry.
• Students will understand and apply scientific concepts, principles, and theories pertaining to the physical setting and living environment and recognize the historical development of ideas in science