NHMU: Boy, Is That Buoyant!

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.

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?