This is the fourth Investigation of the LabLearner CELL Properties of Matter. In it, students will begin to explore the relationship between mass, weight, and density.

Class Materials:

• 1 empty soda bottle or another container that will hold 1 liter of water 
• small wooden objects such as a pencil or metric ruler 
• small container filled with water 

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A. Use the following questions to prompt discussion of Investigation 3.

1. Ask students:  What property of matter did we find affects whether or not an object will float or sink? Students should indicate that density determines floating and sinking.

2. Ask students:  How did Investigation 3 lead us to that conclusion? Students should indicate that they tested whether objects floated or sank and compared sinking and floating to the property of density.

B. Tell students:  In Investigation 3, we tested objects to see if they floated or sank.  Let’s think of some everyday objects that float and sink.  Ask students the following questions to prompt discussion:

1. Ask students: What objects float in water? Students should indicate objects such as boats, pool rafts and toys, sticks, rubber duckies or other bath toys, etc. 

Students should record their answers in Problem 1 of the Student Data Record.

2. Ask students: What kinds of materials are those objects made of? Students should indicate materials such as wood, plastic, foam, etc. 

Students should record their answers in Problem 2 of the Student Data Record.

3. Ask students: What objects sink in water? Student answers may vary.  Students should indicate items such as rocks, marbles, anchors, seashells, etc. 

Students should record their answers in Problem 3 of the Student Data Record.

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4. Ask students: What kinds of materials are those objects made of? Student answers may vary. Students should indicate materials such as rock, metal, glass, etc. 

Students should record their answers in Problem 4 of the Student Data Record.

5. Ask students: Does a log sink or float in water? Student answers may vary. Students should indicate a log floats.  

6. Ask students: What material is a log made of? Students should indicate that it is made of wood.

7. Ask students: Can you find something in the classroom that is made of wood? Students’ answers may vary. Students should indicate items such as a ruler or pencil.

8. Pick up the pencil (or another wooden object) you have in the front of the classroom.  Ask students:  If the log floats and it is made of wood, do you think a pencil made of wood will also float? Yes.

a. Test the pencil in the water to demonstrate that it floats.  If the container you have is too small for the whole pencil, break a piece of the pencil off so that it will fit into the container.

b. Ask students: Do you think that what an object is made of, can affect its density? Student answers may vary. 

Encourage students to recall the density particles diagram from the previous investigation. Point out that in the previous investigation, they examined objects of different densities that were also made of different substances. Therefore, the particles could be particles of different substances. Direct student’s to the Scientist’s Glossary for density if necessary.

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C. Continue reviewing floating and sinking with the students. Students will conduct a scavenger hunt for objects around the classroom that will float and sink. 

1. Divide the class into cooperative groups of 4 to 6 students.

2. Tell students:  You are going on a scavenger hunt around the classroom.  As a group, you need to find two small objects: one that will float, and one that will sink.  

Remind students that the objects need to be small enough to fit into the container of water.  Also, they have to be able to be tested in water.  An example of something they could test would be a pen or binder clip. 

If students are having difficulty finding objects, other items they could test include mechanical pencils, pens, rubber bands, a piece of paper, a ruler, eraser, chalk, etc.

3. After students have gathered the objects, ask them to hold them up in the air.  If any of the objects are too large, or can not be placed in water, have the group find another object.  Once objects are collected, have students draw or write what they have found in Problem 6 of their Student Data Record.

4. Direct students to predict which object will float and which object will sink in Problem 6 of their Student Data Record.

5. Ask students:  What do we know determines floating and sinking from Investigation 3? Students should indicate density.

6. Ask students: Which of your items do you think is the most dense? 

Ask students to hold up the most dense object that their group was able to find.

7. Ask students:  Why do you think that item is the most dense? Students’ answers may vary.  Students should indicate reasons such as the weight, material, shape, or size of the object.

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8. Ask students:  Do you think that item will float or sink? Students should indicate that the object will sink in water.  

Direct students to record their answers in Problem 6 of their Student Data Record.

9. Have students bring the objects to the front of the class one at a time to test the objects in water while the rest of the class observes.  Direct students of that group to record whether the object floated or sank in their Student Data Record.

10. Ask students: Which of your items do you think is the least dense?  

Ask students to hold up the least dense object.

11. Ask students:  Why do you think that item is the least dense? Students’ answers may vary.  Students should indicate reasons such as the weight, material, shape, or size of the object.

12. Ask students:  Do you think that item will float or sink? Direct students to record their answers in Problem 6 of their Student Data Record.

13. Have students bring the objects to the front of class one at a time to test the objects in the water while the rest of the class observes.  Direct students of that group to record whether the object floated or sank in the test column of the table in Problem 6.

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D. Introduce and discuss the concept of weight with the students.

1. Ask each student to compare the weights of the two objects for their group by holding one object in each hand.

2. Ask students:  What properties of the objects do you think relate to density? Do you think heavier objects are more dense? Are lighter objects less dense? Student answers may vary.  Students should indicate properties such as the material, size, or weight.

3. Ask students:  What is weight?  Choose a volunteer to read the definition for the Scientist’s Glossary.

“Weight:  A measure of how heavy an object is.”

4. Ask students:  How do we measure weight? Student answers may vary.  Students should indicate you use a scale and measure weight in pounds!

5. Tell students:  We can also measure weight in kilograms (kg).

6. Ask students:  How much is a kg? Student answers may vary.  

Tell students:  1 kg is equal to the mass of 1 liter of water. 

To give you a better idea of what a kg is, one liter of water weighs one kg.  Pass around the container with one liter of water so that students can feel how heavy it is.

7. Refer to this slide to show students the weights of various different objects.

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E. Continue to discuss weight and how the students will be investigating weight in the lab.

1. Ask students:  Does weight tell you about the volume of an object? Student answers may vary.  

Tell students that generally bigger things weigh more, but sometimes a small object can weigh more than a larger one.

2. Ask students:  Does weight tell you about the density of an object? Student answers may vary.  

Instruct students that heavier objects tend to sink, but that is not always the rule.  They will explore weight and density further in the lab.

3. Ask students:  What tool can we use in the lab to compare the weights of different objects? Students should indicate that they can compare the weights of different objects using the pan balance.  Inform students they will be using a pan balance in the lab to compare the weights of different objects.

4. Ask students:  Will the pan balance help you determine density? Student answers may vary.

F. Tell students they will investigate weight and how it affects floating and sinking.  As they perform their experiments they should think about the following three questions:

Are objects with the largest volume, the heaviest?

Are objects with the least volume, the lightest?

Does weight effect floating and sinking?