This is the third Investigation of the LabLearner CELL Exploring Density. In it, students will begin to explore the density of water and why some objects float on water while other sink.

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A.  Encourage students to recall important concepts from the first two investigations.

Explain to students that Investigation Three begins by using a Cognitive Tool to think about what they already know about properties of matter.  Encourage students to try to remember activities and experiments in Investigations One and Two. 

Ask students to recall properties of a solid, liquid, and gas from Investigation One. Student answers may vary. Students should recall that solids, liquids and gases have volume and take up space. Investigation One involved examining different forms of water in three states of matter: ice, liquid water, and water vapor (gas).

Ask students to recall the property of volume from Investigation Two.  Discuss how the objects displaced the water. Student answers may vary. Students should recall that they examined differences in the volume of gram cubes and metal cubes, but found that the volume of each was equal to the volume of water that was displaced. Students found that when the shape of an object changes, the volume remains the same.  Encourage students to recall that volume is measured in milliliters.

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B. Tell students they will be investigating another property of water: density.

1. Tell students: density is a property of matter that can be difficult to observe with their eyes, but that there are ways to help them understand it.

2. Refer students to their Scientist’s Glossary. Ask a volunteer to read the definition of density and the definition of particle.

Density:  how tightly packed the particles of a substance are.

Particle: a small piece of matter.

Tell students:  When something is more dense, the particles are really close together.  When something is less dense, the particles are father apart.  Point out the closeness and high number of particles in the more dense circle.  Point out the space and low number of particles in the less dense circle.

3. Direct students: to Problem 1 in their Student Data Record.

a. Tell students:  We are going to show more dense and less dense.

b. Tell students: Remember when something is more dense the particles are really close together.  Look at the first circle with particles that are close together.

c. Instruct students to fill in the first circle in Problem 1.

d. Tell students:  As we go across the circles, each one gets less dense. Point out the second circle in the sequence at the bottom of the slide.

Tell students: less dense means the particles are father apart. Let’s fill in the second circle with particles that are less dense than the first circle.

e. Direct students to fill in the remaining circles, getting less dense as they go along.

f. Point out to students that all five of the the circles in Problem 1 in their Student Data Record represent the same volume. That is, the circles would all take up the same amount of space in the classroom if they were real objects. However, there would be more particles in the more dense circles and fewer particles in the less dense circles.

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C. Direct students to get out their Stepping Stones from Investigation Two. Divide students into five cooperative groups.  Explain that they will be doing an activity to show More Dense and Less Dense.

1. Have students lay out a 4 x 2 block of Stepping Stones as shown on the slide.

2. Tell students:  One way to show different densities of objects is to have more or less particles. You are going to be particles in an object, and the Stepping Stones represent the object.

3. Instruct students to have 4 group members stand in the square so that one person’s foot is on each square.

4. Tell students:  Let’s practice More Dense.

a. Instruct students: to have the 5th group member join the other students on the stepping stones.

b. Tell students:  We started with 4 particles. How did adding a person represent more dense? Students should indicate that adding a person represented the addition of a particle. More particles in the same space would indicate a higher density.

5. Tell students:  Let’s practice Less Dense.

a. Instruct students to have 2 group members leave the stepping stones.

b. Tell students:   You had 5 particles, and now you have 3 particles.  How did this represent less dense? Students should indicate that removing a person represented the removal of a particle. Fewer particles in the same space would indicate a lower density.

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6. Tell students:  Now let’s practice changing the density of the substance. When I say More Dense, you have to add particles.  When I say Less Dense you have to take away particles from your object.  You can choose how many particles to add or take away.  Ready?

7. Direct students to change the density of their objects.  Say:

More Dense

Less Dense

Less Dense

More Dense

Less Dense

More Dense

More Dense

8. Direct students to put the Stepping Stones away and to return to their seats.

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D. Discuss how things can sink and float in liquids.  Direct students to record their answers in Problems 2-4 their Student Data Record.

1. Ask students: What kinds of objects float in water? Student answers may vary.  Students should indicate items such as rafts, ice, boats, etc.

2. Ask students: What kinds of objects sink in water? Student answers may vary.  Students should indicate items such as rocks, marbles, bricks, etc.

3. Ask students: What do you think determines if an object will float or sink in water? Student answers may vary.  Students may answer that size or weight determines whether an object floats or sinks.

E. Tell students: they will be conducting several experiments that will increase their understanding of floating and sinking.  As they conduct their experiments, they should think about the following questions:

Will ice float in oil?

How does the density of a solid effect floating and sinking?

Can density change?