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Title: Fluid Density and Buoyancy
Principle(s) Investigated: Density, buoyancy, Archimedes' Principal
Standards : Grade 8 Standards 8 and 9
All objects experience a buoyant force when immersed in a fluid. As a basis for understanding this concept:
c: Students know the buoyant force on an object in a fluid is an upward force equal to the weight of the fluid the object has displaced.
d. Students know how to predict whether an object will float or sink.
9. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will:
a. Plan and conduct a scientific investigation to test a hypothesis.
Materials: Salt, eggs, beakers, water
Student prior knowledge: Knowledge of what density is, how density is calculated, knowledge of what buoyancy is,
Explanation: This experiment is going to give secondary students a solid understanding of what Archimedes' Principal is, applications of density, buoyancy, and help explain real world examples of density and buoyancy in action. We had previously experimented with density (D= mass/volume) and know that the mass of an object is greater than the density of the fluid it will sink, and if the mass of an object is less than the density of it's fluid it will float. However not all water is the same. Salt water and fresh water have differing amounts of density. This experiment will help show students which has more density, the difference in buoyancy between salt water and fresh water and how the differences effect man and nature.
Students are to do the following in self created groups of 4 students:
1. Fill the beaker approximately half full with tap water and record the water level.
2. Place one egg into the beaker.
3. Record the water level
4. SLOWLY pour salt into the beaker until the egg is suspended above the bottom of the beaker, but below the surface of the water.
5. Answer question 1 as a group and record your answers.
6. Make the egg rise by either adding water or salt.
7. Sink the egg by either adding water or salt.
Questions & Answers:
1. Should more solute (salt) or solvent (water) be added to raise a submerged egg to the surface? Explain your answer.
2. Will a cargo ship ride higher in freshwater or saltwater?
3. Why would oil companies flood oil wells with salt water to increase production?
Applications to Everyday Life:
Explains why icebergs can be deceptively dangerous.
Explains why cargo ships have to adjust their specifications depending on what type of water they are in.
Explains why salmon swim up rivers to spawn even though they live most of their lives in the ocean.
Photographs:
Videos: http://www.youtube.com/watch?feature=player_embedded&v=2TAX0bgWIps Titanic
http://www.youtube.com/watch?feature=player_detailpage&v=5DqjsWsY8-g Salmon Life Cycle
http://www.youtube.com/watch?feature=player_detailpage&v=BLPPp9XT8Y8 Bear Gryls in Alaska
References: Cunningham, J., Herr, N., (1994) Hands-On Physics Activites: With Real Life Applications. San Francisco: Jossey-Bass
United States Department of Labor. Oil and Gas Well Drilling and Servicing eTool. (2001) http://www.osha.gov/SLTC/etools/oilandgas/glossary_of_terms/glossary_of_terms_p.html (2012, 3, 12)
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