This is the final regular Investigation in the LabLearner CELL Properties of Matter. In it, students explored the concept of Buoyancy.

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A. Begin the analysis of the Lab experiments by discussing what students explored during Investigation Five.  The following questions can be used to prompt a discussion of these experiments.  Students may refer to their Student Data Records if necessary.

1. Ask students: What was the property (or properties) of matter being investigated in this lab? Student answers may vary.  Students should indicate buoyancy was being investigated. They may also indicate density or other properties.

2. Ask students: What were the main questions asked during the Lab? Students were asked the following questions.  Can you change the buoyancy of clay? Can you change the buoyancy of a falcon tube? Can you change the buoyancy of a weigh dish?

3. Ask students: Can you describe what you did in your experiments to answer the questions? Students should suggest that to answer the questions, they came up with ideas and tested them for each object.

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B. Continue to analyze the Lab experiments by reviewing Trial 1 with students.  The following questions may be included to prompt student discussion: 

1. Ask students: What happened to the clay ball in the water?  Why? Students should indicate that the clay ball sank in water.  It was more dense than water and not buoyant.

2. Ask students: Were you able to make the clay float? Students should indicate yes.  

If some groups were unable to make the clay float, use the next question to review how it is possible to make the clay float.

3. Ask students: What shape made the clay float? Students should indicate that were able to make the clay float by making it into a bowl or boat shape.

4. Ask students: What was added to the clay in the shape that floated? Students should indicate that air was added to the clay because there was air inside the bowl/boat shape.

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C. Continue to analyze the Lab experiments by reviewing Trial 2 with students.  The following questions may be included to prompt student discussion: 

1. Ask students: What happened to the centrifuge tube in water?  Why? Students should indicate that the centrifuge tube floated in water.  It was less dense than water and buoyant.

2. Ask students: Were you able to make the centrifuge tube sink? Students should indicate yes.  

If some groups were unable to make the centrifuge tube sink, use the next question to review how it is possible to make it sink.

3. Ask students: How did you make the centrifuge tube sink? Examples may include taking off the lid and filling the tube with water or by adding metal nuts to the tub.  Students may have also found other ways to make the tube sink.

4. Ask students: What was added to the centrifuge tube when it sank? Student answers may vary. Two possibilities may have included filling the tube with water or with metal nuts.

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D. Continue to analyze the Lab experiments by reviewing Trial 3 with students.  The following questions may be included to prompt student discussion: 

1. Ask students: What happened to the weigh dish in water?  Why? Students should indicate that the weigh dish floated in water.  It was less dense than water and buoyant.

2. Ask students: Were you able to make the weigh dish sink? Students should indicate yes.

3. Ask students: How did you make the weigh dish sink? Students should indicate that they were able to make it sink by placing the 200g weight in it.

4. Ask students: What was added to the weigh dish when it sank? Students should indicate that the 200 g weight was added.

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E. Guide the students in analyzing buoyancy.

1. Ask students: Were you able to change the buoyancy of the objects?  Yes.

2. Ask students: Why do you think the buoyancy changed?  Student answers may vary.

3. Explain to students that air played a role in the buoyancy of the objects.  Remind students that when the clay was made into a bowl shape, the bowl was actually filled with air.  

The centrifuge tube was buoyant when it was filled with air.  Also, the weighing dish was buoyant when it was filled with only air.

4. OPTIONAL DEMONSTRATION: Tell students:  Watch what happens.  Place the drinking straw in the cup of water. Blow air into the straw so that bubbles are formed in the cup of water.

a. Ask students:  What happens to the bubbles of air in the water? Students should indicate that the bubbles float to the top of the water.

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1. Lead students in drawing a conclusion about the density of air.

a. Ask students:  Did objects that were filled with air float or sink in the lab? Students should indicate that adding air made an object float.

b. Ask students:  Is air more or less dense than water?  How do you know? Students should indicate that air is less dense than water because adding air to objects makes them float. If something floats in water, it is less dense than water. Also, the bubbles floated in the water.

c. Ask students:  Does adding a less dense substance to something make it more buoyant? Students should indicate it makes something more buoyant.

2. Lead students in drawing a conclusion about buoyancy.

a. Ask students:  What happened when we added the 200 g weight to the weighing dish? Students should indicate the weighing dish sank in the water.

b. Ask students: Was the 200 g weight more or less dense than water?  How do you know? Students should indicate that the weight is more dense than water because adding the weight to weigh dish made it sink. If something sinks in water, it is more dense than water.

c. Ask students:  Does adding a more dense substance to something make it less buoyant? Students should indicate it makes something less buoyant.

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F. Refer to this Concept Map and direct students to revisit the concept map from the PreLab.

1. Tell students:  We can fill in the last line under buoyancy using the information we have learned from the Investigation.

2. Ask students:  Can buoyancy be changed? Yes.  

Fill in number 3 under buoyancy with “Buoyancy can be changed”.

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G. Guide students in understanding why buoyancy is important.

1. Ask students:  Why is buoyancy important? Student answers may vary.

2. Ask students:  Can you think of an object that needs to be buoyant? Student answers may vary.  Students should indicate objects such as life vests and boats.

3. Ask students:  Can you think of something that should not be buoyant? Student answers may vary.  Students should indicate objects such as an anchor or the drain plug in the bathtub.

H. Explain to students that you would like them to think about what they have learned about buoyancy.  They will be using what they know to help solve a problem.

1. Tell students:  The weigh dish we used in the lab was like a small boat.  When the boat had a cargo of the gram bear, it floated.  When the boat had a cargo of the 200 g weight, it sank.  Now you are going to hear a story about a captain with a large boat.  You must help him decide which cargo his boat can carry.

2. Tell students the following story:

A boat captain makes his living by delivering cargo overseas.  Two different businessmen have asked the boat captain to carry their merchandise to another country.  The men both need all of their cargo to go in one trip.  The cargo will fill the captain’s boat to the very top.  The first man asked the captain to carry vegetable oil overseas.  The second man asked the captain to carry a load of metal marbles overseas.  Which cargo, oil or marbles, should the captain agree to carry in his boat?  Why?

Students should indicate that the captain should carry the oil.  Oil is less dense than water.  If the boat is filled with oil, it will be buoyant.  Marbles are more dense than water. If the captain fills his boat completely with marbles, the buoyancy of the boat could change and it could sink.