This is the final regular Investigation of the LabLearner CELL Properties of Matter. In it, students will begin to explore the concept of buoyancy and why some objects float on water while others sink.

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A. Begin this investigation by reviewing previous investigations.  Direct students to refer to their previous Scientist Data Records.  Use the following questions to prompt discussion with students:

1. Ask students: What are the three states of matter? Students should indicate solid, liquid, and gas.

2. Ask students: What are some properties of each state of matter? Student answers may vary.  Students should indicate properties such as a solid has a definite shape, liquids taking the shape of their container, gases are difficult to see, etc.

3. Ask students: What properties of matter have we examined in the lab? Student answers may vary.  Students should indicate properties such as volume, density, and weight.

4. Ask students: How did we measure these properties? Student answers may vary.  Students should indicate they used water to measure volume, they tested density by testing floating and sinking, and they used the pan balance to examine weight.

5. Ask students: Can containers with different shapes hold the same volume of water? Students should indicate that it is possible for containers of different shapes to hold the same volume of water?

6. Ask students: How are estimating and measuring different? Students should indicate that estimating is a guess and is not always accurate, but when measuring is accurate and ensures that everyone gets the same answers.

7. Ask students: What property determines floating and sinking? Density

8. Ask students: What is weight? Weight is how heavy something is.

9. Ask students: Is weight the same as density? No.

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B. To organize the information students have obtained from the previous Investigations and introduce the next Investigation, students will complete a concept map.

1. Instruct students to get into groups of 4-6 students.

2. Tell students that they will discuss one property of matter. Encourage students to review previous Student Data Records to locate information about the property. They should record their answers in Problem 1.

3. Assign each group the property of volume, density, or weight. Buoyancy will be discussed later as a class to lead into the lab.  Allow students 10-15 minutes to complete the task.

4. Ask each group to share how they answered the questions about each property.  As you review each property, fill in the concept map on the board.  Direct students to fill in their concept map in Problem 2 of their Student Data Records. 

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Refer to this slide for reference. Use it to draw a similar Concept Map on the board so that you can add student ideas to it with the class.

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Direct students to recall what they already know about density:

• Ask students: What happens to objects that are less dense than water? Students should indicate that they float in water.

• Ask students: What happens to objects that are more dense than water? Students should indicate that they sink in water.

Ask students to recall the ice and oil experiment from Investigation 3. 

•Ask students: Did the ice cube float or sink in oil?  Why? Students should indicate that the ice cube floated because it was less dense than oil.

• Ask students: As the ice melted, did the water float or sink in the oil?  Why? Students should indicate that the water sank because it was more dense than oil.

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C. Introduce buoyancy to the students.

1. Ask students:  What is buoyancy?  Choose a volunteer to read the definition of buoyancy from the Scientist’s Glossary.

Buoyancy:  something’s ability to float.

2. Ask students:  What happened to the buoyancy of water as it changed states from a solid to a liquid? Students should indicate that it became less buoyant.

3. Explain that the ice was buoyant because it floated in the oil.  The water was not buoyant because it sank in the oil.

4. Ask students:  It is possible to change the buoyancy of an object.  How do you think buoyancy can be changed? Student answers may vary.  

Tell students:  We will explore in the lab different ways to change buoyancy.

5. Tell students:  Let’s fill in buoyancy in our concept maps.  

Direct students to fill in their Student Data Record as you fill in the concept map with the following information:

• Buoyancy is the ability of something to float.

• Buoyancy is related to density.

6. Number 3 under buoyancy on the Concept Map will be filled in during the post-lab when students learn that adding a substance such as air can change buoyancy.  Tell students:  We will fill in number 3 under buoyancy later.

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D. Tell students they will be conducting experiments to test the buoyancy of different objects. As they conduct their experiments, they should think about the following questions:

• Can you change the buoyancy of clay?

• Can you change the buoyancy of a balloon?

• Can you change the buoyancy of a centrifuge tube?