Finding Nemo in the Density Column

Teacher’s Instructions

Description: In this activity, students will use common liquids of differing densities to create a layered column. They will then find the density of their “fish” (beads strung together with twine), and add the appropriate weight to the string to have the fish float between two specified layers.

Learning Goals:

Observe the density of liquids

Use problem solving skills

Understand the concept of density including how to find and use this property of a substance.

Recommended Grades:

3-7

Estimated Time Required:

45-60 minutes

Key Concepts and Terms:

Mass – the amount of matter in an object

Volume – the amount of space an object occupies

Density – the property derived by the quotient of an object’s mass and volume

Displacement – the difference in liquid levels when a solid is submerged in a fixed container.

What happens and why:

Due to the different densities, the liquids float on each other and naturally separate into distinct layers. Since these densities are known, the density of the fish can be adjusted by adding weights to make the fish float between the desired levels.

Materials Needed:

Per Student or Group:

1 tall clear cup (16 oz plastic)

Cup to measure layers(6 oz plastic)

Calculator

Layers:

-Molasses

-Light Corn Syrup

-Syrup (Mrs. Butterworth’s)

-Dish Soap (Palmolive)

-Vegetable oil

-Baby Oil

Fish:

-Twine

-Beads

Safety Information:

Glassware is fragile

General Outline:

  1. Discuss density with class (why some things float and some things sink)
  2. Distribute fish and cups to groups
  3. Students weigh the measuring cup and then proceed to find the density of each liquid by massing it and then dividing by the volume.
  4. After finding the volume of a liquid, students add it carefully to the large plastic cup.
  5. Students then find the density of their fish (using volume by displacement)
  6. Students determine how many washers it will take to get their fish in between each level and then test their predictions.
  7. Short discussion of density (mention the Eureka story of the gold crown)
  8. Clean hands and equipment in the bucket of soapy water. Dispose of cups

Notes:

For grades that have not covered division, do not calculate density, simply enforce the idea that density has two parts: mass and volume (use these in simpler terms though)

Grades older than 5th grade need not be as closely supervised as younger students who have trouble recording data on tables.

For all grades, some good examples of density are Saturn’s density (less than water, so it would float if one could find a source of water big enough) and Archimedes’s Eureka exclamation as figured out how to tell that a king’s gold crown had secretly had silver in it when he got into a full bathtub and water overflowed the tub. By discovering volume by displacement he could test the density of the crown and the density of pure gold to determine that the king had been cheated.