Investigating Density in solutions: How can you make an egg float?
Summary
In this interactive demonstration, students will determine how to make an egg float in water.
CollapseLearning Goals
This activity is designed so students will see the effect of density on floating/sinking. Students will need to have a preliminary understanding of the terms float and sink. They will learn that objects that are more dense than the liquid they are in sink, and objects that are less dense than the liquid they are in float. By the end of the lesson, students will understand that density and weight are different, and that density matters in floatation.
Context for Use
This activity is designed for upper elementary students who have had minimal contact with the term density. It is an introductory demonstration with a structured inquiry component, and can be easily adapted to guided inquiry or total demonstration, dependent on the situation. This lesson will take approximately 45 minutes.
Description and Teaching Materials
Students will view a brief video from Science and the City explaining density (Available on youtube.com). Teachers without access to this video can easily recreate some of the demonstrations, including two different density bowling balls in an aquarium, ice floating in water and sinking in baby oil, and making a Shirley Temple with grenadine and ginger ale.
After viewing the video, the teacher demonstrates one or two live experiences modeling the concept of density, such as oil floating on water, and cold water (with blue food coloring) and hot water (with red food coloring).
Then, the students get to figure out how to float an egg. Each student group needs to have one hard-boiled egg (raw eggs do the same thing, but students have to be a lot more careful), one beaker, and one container of salt. Students should place the egg in fresh water, observe, and note what they see on their paper. Then, they remove the egg from the water. Adding two tablespoons of salt, repeat the experiment and observations. Remove the egg again, add two more tablespoons of salt, and continue to observe. Repeat the process until the egg floats.
Students should note how much salt it takes to float the eggs, and then report back to the class. Ask students to reflect on why the egg floats on salt water, but not fresh water.
After viewing the video, the teacher demonstrates one or two live experiences modeling the concept of density, such as oil floating on water, and cold water (with blue food coloring) and hot water (with red food coloring).
Then, the students get to figure out how to float an egg. Each student group needs to have one hard-boiled egg (raw eggs do the same thing, but students have to be a lot more careful), one beaker, and one container of salt. Students should place the egg in fresh water, observe, and note what they see on their paper. Then, they remove the egg from the water. Adding two tablespoons of salt, repeat the experiment and observations. Remove the egg again, add two more tablespoons of salt, and continue to observe. Repeat the process until the egg floats.
Students should note how much salt it takes to float the eggs, and then report back to the class. Ask students to reflect on why the egg floats on salt water, but not fresh water.
Teaching Notes and Tips
Students often think objects float or sink because they are heavy. It is helpful for students to see the bowling ball demonstration because a floating bowling ball is a discrepant event for students. If they are still struggling with this idea, show another demonstration, this time with a metal object weighing 8 pounds and an 8 pound bowling ball. The smaller object will sink while the bigger floats, even though they weigh the same amount.
Assessment
Students will be asked to explain why a particular object (one they saw demonstrated) sinks or floats in paragraph form. Their answer should contain a brief explanation of the concept of density.
Standards
3.I.A.1 Scientific World View
6.2.A.5 Physical Science, density
6.2.A.5 Physical Science, density