Investigating Floating and Sinking: Density

Steve Knaus
Grade 5
Tanglen Elementary
Hopkins Schools, Minnetonka, MN
Based on the "Lifeboats" Investigation #2: FOSS; Variables.
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Summary

FOSS VARIABLES; Investigation #2: "Lifeboats" deals with capacity (more capacity means more "cargo.") However the true reason that objects float or sink deals with density. While this is an extremely difficult process to understand, fifth and sixth grade students should be able to begin to use and experiment with simple "ideas" to begin to relate how mass and volume interact.

Learning Goals

Students will define mass, volume, and density.
Students will measure mass and volume and with a simple math division problem find density.
Students will graph mass and volume to find a line of density.
Students will make predictions of whether an object will float or sink after finding mass and volume of an object.

Context for Use

Grade 5 or 6 students may study FOSS Variables Investigation #2 "Lifeboats." A class of 28 divided into groups of four would be ideal. After following the lessons of the investigation the teacher can continue with the introduction of volume, mass, and density. Perhaps one or two extra hour long sessions would be enough to enrich this activity. Along with the materials found in the FOSS kit, a scale that would weigh objects in grams would be helpful. (The FOSS measurement kit may have a balance scale.) One may also use larger containers to find the volume of larger objects.

Description and Teaching Materials

MATERIALS
Four boats with different capacities
Large tub or basin
Graduated cylinder, 50ml
Syringe, 50ml
Pennies
Plastic cup with water
Balance scale or electronic science scale (grams)
Graph paper with centimeter grids.
Objects from home that could fit in a small container (you provide or ask students to bring - don't say anything about floating objects or sinking objects)
Container that is calibrated in milliliters (big enough to hold brought in objects)


Lesson One:
After completing the "capacity" part of the "Lifeboats" investigation return to the boats and place the same number of pennies into the boat that caused the boat to sink. Place the boat into the bottom of a basin and fill the boat with water. Remove the water with the syringe and pour into the graduated cylinder. Measure. Subtract the volume of this from the amount of volume from the boat and you'll have the volume of the pennies. Remove the pennies and find their weight on the scale.

Introduce the graph paper by plotting on the horizontal axis the volume of the pennies and on the vertical axis the weight (mass). Connect the plotted points.

Introduce the scientific formula for density as mass divided by volume. When density is greater than one the object will sink. When equal to one or less the object will float.

Lesson Two:
Provide a small object to each group. Have students predict if the object will sink or float. Students should then weigh the object. Students next place the object into a container that shows milliliters on the side and filled with enough water so that when the object is placed into the container it will be covered. Note the change in milliliters. This change will be the object's volume. Take the weight and divide by the volume to find the object's density. When density is greater than one the object will sink. When equal to one or less the object will float. Then place the object into a large tub filled with water to confirm if the object sinks or floats.

Teaching Notes and Tips

An area of confusion would be the use of the word weight and mass. They are different. I like to think of mass as being "all the stuff that makes up the object" while weight is what we place on a scale here on Earth.

Assessment

By determining density using the formula where you able to predict correctly?

Standards

6.II.A.5 - Volume, Mass, Density

References and Resources