Determining Density

Density helps us compare different substances—not just different objects, but the substances of which objects are made. To compare the density of two materials, we consider pieces of each material with the same volume, and compare their masses. To do this without actually chopping pieces out of objects, we divide the mass of each object by its volume.

But science teachers are eager for their students to gain more insights into the property of density, so we have set up several activities that focus on density on the conceptual level.

Activities

Reading: Archimedes & the Case of the Missing Gold

This unit begins with an expertly-illustrated retelling of the classic story of Archimedes' “EUREKA!” moment. He is credited by some for coming up with the idea of determining the volume of an irregularly shaped object by dipping it into water... just as he was dipping himself into the bathtub!

Duration: Approximately 50 minutes

Conversation: The Basics of Density

Students explore a series of slides containing questions that compare a piece of gold with a piece of wood.

Duration: Approximately 40 minutes

Interactive: Heating Up and Spreading Out

Objects' densities can change depending on their conditions. In this activity, students students interact with a simulation of iron atoms heating up.

Duration: Approximately 50 minutes

Lab: Is Putty or Clay More Dense?

In this fun and informal lab, students come up with ways to determine the density of irregularly shaped pieces of clay and putty. Students can then go on to determine whether or not samples are pure (without cutting them open) just as Archimedes did.

Duration: Approximately 70 minutes

Teacher Tune-ups

• How does the density of an object relate to the mass of an object?
• How is liquid displacement used in density measurement?

Student View of Visuals and Activities

Some teachers prefer to have students view the slides and other visual assets in this unit directly instead of projecting them in class. Below is a web page to share with students with links to some of same items that are within in the teacher lesson plans, but without the explanatory text for the teacher.

 

• Student Links to Unit M2 Slides and Other Visuals

Original SciGen Unit

This unit has been adapted from pieces of the three units of the "Introductory Chemistry Concepts" group and "7.2 Does the metric system measure up?" in the Word Generation program led by Catherine Snow (Harvard University) through a SERP collaboration with the Boston Public Schools and other districts in Massachusetts and Maryland.

PDFs of that earlier unit's teacher and student editions are available at the Science Generation Download Center.

density

noun – the ratio of mass to volume

How do differences in density help balloons float in the air?

volume

noun – the amount of space taken up by an object

Is it easier to determine the volume of a brick or a stone?

mass

noun – a measure of the quantity of matter in an object

Imagine you take a trip to the moon on a new spaceship. Would your mass change when you leave Earth?

fluid

noun – a substance that is in a liquid or gaseous phase

Compare and contrast the characteristics of liquid and gaseous fluids.

irregular

adjective—not following a common or expected pattern

From far away the spire looked like a simple cone, but when we got closer we saw that it was quite irregular, covered with random bumps and grooves.

displacement

noun – the space taken up by an object submerged in a fluid

How did Archimedes use displacement to compare a gold bar to the king's new crown?

expand

verb — to spread out, to enlarge

My kickball was a little flat when we were playing outside in the freezing winter air, but as soon as we bring it into the overheated library it should expand to its normal size.

reference point

noun – a starting value for measurement, or basis of comparison

Sailors, nomads, and people on the move in many cultures throughout history have often used the North Star as a reference point in celestial navigation.

Eureka!

interjection—an exclamation expressing the excitement of a discovery or breakthrough, from the Ancient Greek word εὕρηκα “heúrēka” meaning "I found (it)"

After toiling away in my workshop for months, I was so glad when I finally got my invention to work that I cried out, “Eureka!”