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NHMU: Boy, Is That Buoyant!

Group Size:
Large Groups


 

Summary:
Students will learn that salt increases the density of water and creates a condition wherein objects are more buoyant than would be expected under normal conditions.

Main Curriculum Tie:
Science - 4th Grade
Standard 1 Objective 1

Describe the relationship between heat energy, evaporation and condensation of water on Earth

Career Connections:

  • Environmental Scientist
  • Forester/Conservationist

Materials:

  • 3 clean peanut butter or mayonnaise jars with lids
  • 3 golf balls
  • Table salt (about one 26 ounce package)
  • Pasta server or large slotted spoon
  • Masking tape and/or permanent marker
  • Hot water
  • Paper towels or newspaper

Instructional Procedures:

  • Label each jar with masking tape (if you want to reuse your jars) or marker as follows:
    • 1st jar: Gunnison Bay or North arm
    • 2nd jar: Gilbert Bay or South arm
    • 3rd jar: Fresh water

  • Fill the first jar 28% full of table salt, add hot water (for super-saturation) to 1 inch below lid level, replace lid tightly and shake (to dissolve salt as much as possible).
  • Fill the second jar 6 to 11% full of table salt and repeat what you did with the first jar.
  • Fill the third jar with room temperature water to equal the level of the other jars.
  • When water has cooled and salt has dissolved as much as possible (the water in the 1st and 2nd jars may become super-saturated and be unable to dissolve all of the salt) take the lid off the jars and place side by side on paper towels or newspaper.
  • Have students drop a golf ball into each jar with the slotted spoon and record or graph their observations.
  • Ask students to interpret their observations out loud or on paper.
  • Experiment may be repeated and different variables introduced (drop objects of different size, shape or density and compare results to the golf ball, or, what % of salt can be absorbed in the jar of water before it becomes saturated, etc).
Questions for Discussion & Discovery:
  • Which of the jars (1 or 2) gave results closest to that of fresh water? Why?
  • How did the golf balls react to being placed in each jar? Why?
  • What does it mean to be buoyant or to create buoyancy?
  • Why are the 2 arms of the lake so different in salt concentration?
  • What living things can survive in salty water? At what concentration? How?
  • What other places in the world have similar conditions?

Author:
Utah LessonPlans

Created Date :
Nov 08 2004 11:57 AM

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