Lecture No 32

Scoring Rubric for Cubic Chart

Scoring Rubric for Oral Presentation

Lecture 33

Lecture 34

In grade 8 we are focusing the properties of materials. We want the children to understand the mass

and volume and are able to differentiate between them. We want them to know the density of

materials.

Lecture 35

This lecture is about assessing children prior knowledge. In the class teacher told the students

that she wanted to examine the concepts of children about the state of matter, its volume, mass,

weight and density. Teacher told the students that it was not a test but it was only for the teacher

to know the baseline of the students. Teacher had arranged the six short experiments for the

students. Students had to work in the group of three. Teacher had labelled the tables with

experiment 1, 2 and 3. So that it would be easier for the students to record their findings in the

worksheets accordingly. Teacher told the students that she had given all the clear instructions in

the worksheets but if they had any questions that might ask. Teacher told the students that they

could give 5 to 7 minutes to one experiment. Because these were the short inquiries so there was

no need to spend more time on experiments. At the end teacher told them that she would switch

over the groups.

During the above first inquiry teacher wrote the word bank on the white board related to the

properties of matter so that if the children had any difficulty they could understand it easily. In

the first inquiry children were observing, discussing and recording.

This was a short inquiry and children did not have any difficulty during this inquiry.

Students had some problem while putting the clay into the water. They were not putting the clay

gently into the water and it was sinking. Teacher had a discussion with the children on that and

they understood that they had to put the clay boat as well as the clay ball gently into the water

and saw the results of floating and sinking.

In this inquiry teacher understood that the notion of the children of volume in milliliter was not

clear.

The end segment was about the students sharing all their findings about the six inquiries. Teacher

must give the students courage to speak. He or she must make them realized that what they are

saying is valuable. And moreover they can learn from each other through sharing.

Lecture 36

This lecture focus on the communication and literacy skills of the students.

Children Ideas

The first student teacher discussion was focusing the communication skills through drawings. This was

the new idea for the children therefore teacher modeled how drawings convey the messages. In the

inquiry of floating and sinking teacher examined that the ideas of students about mass volume and

weight were confusing. All the class had the assumption that because the weight of clay ball was more

than the clay boat so it sank. But teacher challenged their assumption. She put an aluminum foil into the

water and it sank although it was also light weighted. Constructive criticism is the integral part of the

science experiments and teacher must encourage them. Teacher also told the students that the most

important thing in the class discussion is that students must not interrupt each other during the

discussions. Everyone will have his or her own time to talk. It is important to disagree but let the person

talk and give the reason for his or her perspective. Students thought that mass and volume were the

same things. Teacher challenged their assumption she dis the experiment in front of the students that

although sand mass was more than the tea leaves yet the volume of the tea leaves was more than the

sand.

Lecture 38

This lecture will focus on the Phase “B” of the learning sequence template.

In the class activity teacher introduced the length notion. For the measurement of length we use the

metric rule.

Teacher asked the above questions to the students that a meter rule can measure the length. The

maximum length it can measure is 1 meter and the minimum length it can measure is 1 millimeter. Then

the teacher told the students to draw a line of 1 centimeter. For the fifth question children data was as

follow:

Teacher also elaborated how to decompose the numbers at the end.

Lecture 38

This lecture will focus on the Phase “B” of the learning sequence template.

In the class activity teacher introduced the length notion. For the measurement of length we use the

metric rule.

Teacher asked the above questions to the students that a meter rule can measure the length. The

maximum length it can measure is 1 meter and the minimum length it can measure is 1 millimeter. Then

the teacher told the students to draw a line of 1 centimeter. For the fifth question children data was as

follow:

Teacher also elaborated how to decompose the numbers at the end.

Lecture 38

This lecture will focus on the Phase “B” of the learning sequence template.

In the class activity teacher introduced the length notion. For the measurement of length we use the

metric rule.

Teacher asked the above questions to the students that a meter rule can measure the length. The

maximum length it can measure is 1 meter and the minimum length it can measure is 1 millimeter. Then

the teacher told the students to draw a line of 1 centimeter. For the fifth question children data was as

follow:

Teacher also elaborated how to decompose the numbers at the end.

The Science Teacher58

Using sports balls to confront students’ naive conceptions about density

Deborah Herrington and Pamela Scott

With Team Density

Get in the Game

Keywords: Density

at www.scilinks.org

Enter code: TST041101

A floating bowling ball? No way! There is no bet-ter way to get students’ attention and reinforce the need for conceptual understanding than with a discrepant event like this. Density is a central

concept in chemistry and physical science from middle school to college. But often, particularly at the high school and col-lege levels, we think students understand density simply be-cause they can solve density problems.

April/May 2011 59

Get in the Game With Team Density

However, just because a student can recite the density formula—“density equals mass over volume”—does not mean that he or she understands the concept. In this article, we describe an activity in which students explore the rela-tionship among the mass, volume, and density of various sports balls. Students are forced to confront their naive conceptions of density and develop conceptual comprehen-sion of this concept.

B a c k g ro u n dIn our experience teaching high school and college chemis-try, we have found that most students can solve mathemati-cal density problems, but are at a loss when asked to explain how a Cartesian diver works. This is not surprising, given that density is a complex concept involving the interaction of two variables: mass and volume. Students often have sev-eral naive conceptions of density; two of the most common are that

more massive objects are denser, regardless of their 1. volume (i.e., the confusion of mass and density) (Kind 2004; Schmidt 1997) and thatobjects float because they are light (i.e., no regard for 2. volume or density) (Krnel, Watson, and Glazar 1998).

We designed an activity to help students develop con-ceptual understanding of density, in which they investigate the following:

How do mass and volume affect whether an object uu

sinks or floats in water? What is the relationship between density and sinking uu

or floating?

This activity is based on the “Floating Bowling Balls” activity (Steve Spangler Science 2010) and a series of density activities designed for grades 5–8 (Moyer, Hackett, and Everett 2007). I (Herrington) use this activity in a prepa-ratory college chemistry course for preservice elementary teachers, but it can be adapted for middle and high school classes as well. Student and teacher guides for this activity are available online (see “On the web”).

A c t i v i t y d e s i g n To introduce the activity, I present students with a scenario in which a sporting goods manufacturer is considering a new production line for balls, and needs help collecting and analyzing data. Before taking any measurements, students have to qualitatively evaluate the relative masses and volumes of nine different sports balls—softballs, soc-cer balls, marbles, golf balls, Ping-Pong balls, racquet-balls, cue balls, tennis balls, and 3.6 kg (8 lb.) medicine balls—and use this information to predict which will float in water and which will sink. Students must also explain

the rationale behind their predictions. Most students base their predictions on the objects’ masses or on personal ex-perience. A few also mention density.

After making qualitative observations and predictions, I divide students into teams of two. Each pair is assigned two or three different balls and asked to measure the mass and circumference of each. They then use the circumfer-ence and the formulas provided (C=2πr and V=4/3πr3) to calculate the volume of each ball.

Teams share their data in a class table—this provides multiple trials for each ball and allows those with incorrect calculations to immediately see their errors. Figure 1 (p. 60) shows sample student data on mass and volume. Compiling data on the board or computer also provides a good stopping point for class discussion.

At this point in the activity, teachers may want to discuss significant figures for measurement. For example, I have found that students often do not read their measuring tapes to two decimal places, even though the precision of the in-strument allows it. We also discuss how students’ predicted order of masses and volumes compares with their measured values. Students have difficulty with the qualitative order of masses, particularly when distinguishing the difference between the cue ball and the softball. Many think the cue ball is more massive, when in fact the softball is.

This is also a good opportunity for a whole-class discus-sion about which balls students think will sink and which will float. Some of the balls (e.g., golf balls) have densities close to that of water, so imprecise measurements can lead to discrepant results. For example, a student group might predict that a ball will float based on imprecise measure-ments, only later to find (experimentally) that it sinks.

Te s t i n g Next, students test each ball in water. A large garbage can partially filled with water works well. Students can share one garbage can, or if there are enough garbage cans and balls, groups of 8–10 students can test at stations. Large plastic storage containers also work.

After testing the balls, it is important to discuss the results as a class. For example, in my class, several teams predicted that the medicine ball would float. When asked why, one student told me she had used medicine balls in the pool during water polo practice. Fortunately, a bowl-

Car tes ian d ivers . A Cartesian diver is composed of a plastic water or soda bottle containing a neutral buoyancy object—such as a partially filled eyedropper—and filled to the top with water. As you squeeze the bottle, the “diver” goes down; and as you release it, the diver comes back up. Changes in the diver’s density account for this.

e

The Science Teacher60 The Science Teacher60

F i g u r e 1

Sample student mass and volume data for sports balls.

Type of ball Marble

Ping-Pong ball

Golf ball

Tennis ball Softball

Cue ball

Soccer ball

Medicine ball Racquetball

Average mass (g)

5.36 2.54 44.95 55.67 189.95 185.04 275.19 3,613 40.95

Average volume (cm3)

2.54 35.40 43.40 145.4 498.2 105.6 4,537 5,996 99.33

Average density (g/cm3)

2.11 0.0718 1.036 0.3829 0.3813 1.752 0.06065 0.6026 0.4123

(Note: A kilogram scale was needed to obtain the mass of the medicine ball.)

ing ball of about the same size and mass was available. Although I told students it was the same mass and volume as the medicine ball, they all thought it would sink. Their justification was that the medicine ball floated because it was made of rubber—demonstrating students’ ability to rationalize observations to fit their naive conceptions. The look of shock on students’ faces when the bowling ball floated was priceless! (Note: It is best to use a 3.6 kg [8 lb.] bowling ball because it floats fairly high. Bowling balls that weigh more than 5.4 kg [12 lb.] will sink.)

U n d e r s t a n d i n g d e n s i t yStudents then return to their respective work areas to explain any differences between their predictions and their measurements. They are asked to look at two balls of approximately the same mass—one that sinks and one that floats—and compare their volumes. Similarly, they must find two balls with approximately the same volume—again, one that sinks and one that floats—and compare their relative masses. This exercise helps students realize that they have to use mass and volume to determine whether a ball will sink or float—the core concept of density.

After introducing the formula for density and the common units (g/ml and g/cm3), students use their data to calculate the densities of each ball, and to compare the densities of the balls that float to the ones that sink. Students notice that the balls that sink have higher densities than the ones that float. When given the density of water, they notice that the balls that sink have densities greater than that of water, and the balls that float have densities lower than water. (Note: Students can also design an experiment to discover the density of water, increasing the inquiry level of this part of the activity.)

Most of my students were surprised to find that the marble was the densest ball and that the marble, cue, and golf balls were all denser than the medicine ball. When they thought about the fact that these higher density balls sank and the medicine ball did not, they realized that this had to be true.

D i s c u s s i o nAfter students complete the activity, I give them a series of discussion and follow-up questions to answer. Some of these questions require students to use the density for-mula to perform calculations. For example, one question

April/May 2011 61

Get in the Game With Team Density

Ac t iv i ty extens ions .Some possible extensions include a performance as-sessment requiring students to see how many pen-nies they can float on a piece of aluminum foil or whether they can make a piece of modeling clay sink or float. This can lead to a discussion about why ships float and be used as a precursor to an activity in which students explore the buoyant force of wa-ter, such as the one Waugh (2007) describes.

Students can also be asked to predict which soft-drink can will float in water: diet or regular? If students understand their previous investigations and the meaning of density, they will correctly predict that the diet-soda can will float; they can then test this to confirm their prediction. Or, students can design a procedure to make a golf ball float by adding salt to the water.

Still, if that is not enough, think about the im-portance of density in flying. If you ask students to compare the density of humid air and dry air, most will tell you humid air is denser. However, Isaac Newton discovered that humid air is less dense than dry air, a phenomenon he wrote about in his 1704 book Opticks. This is because, at a fixed temperature and pressure, the number of gas molecules in a giv-en volume of air is constant. As humidity increases, heavier nitrogen and oxygen gas molecules are re-placed by lighter water molecules, and the density of the air decreases.

tells students that medicine balls vary in mass but are always the same diameter, then asks them to calculate the mass necessary to sink a medicine ball. (Note: The same is true for bowling balls.)

Other questions are more focused on the concept of den-sity as a measure of how much matter is packed into a given volume. For example, one question asks students to explain how and why the density of the air in a hot air balloon de-creases as it is heated. (The answer is that air expands and escapes the balloon, making the air inside the balloon have less mass and therefore be less dense than the surrounding cooler air. Since the air inside the hot air balloon is now less dense than the surrounding air, the balloon floats—for the same reason that the bowling ball floats in water.)

Co n c l u s i o n The concept of density is a challenging one for students. To develop a conceptual understanding of density, they must first confront their naive ideas. Although initially some of my students think this activity is trivial, when they see the floating bowling ball, they realize they need to rethink some of their ideas about density.

After the activity, most students are better able to answer conceptual density questions. Once this activity is complete, I demonstrate—or have students construct—a Cartesian diver made of a ketchup packet inside a bottle of water and ask them to observe what happens when the bottle is squeezed. I then ask them to explain how it works. At this point, all of my students know that it is related to density, and most recognize that the volume has to be changing because the mass cannot. The bowling ball activity has been a great success! ■

Deborah Herrington (herringd@gvsu.edu) is an associate pro-fessor at Grand Valley State University in Allendale, Michigan, and Pamela Scott (pscott@grcc.edu) is a chemistry laboratory instructor and laboratory coordinator for the Physical Science Department at Grand Rapids Community College in Grand Rapids, Michigan.

On the web

Student and teacher guides: www.gvsu.edu/targetinquiry

References

Kind, V. 2004. Beyond appearances: Students’ misconceptions about basic chemical ideas. 2nd ed. A report prepared for the Royal Society of Chemistry. London, United Kingdom. www.rsc.org/images/Misconceptions_update_tcm18-188603.pdf

Krnel, D., R. Watson, and S.A. Glazar. 1998. Survey of research related to the development of the concept of matter. Interna-tional Journal of Science Education 20 (3): 257–289.

Moyer, R.H., J.K. Hackett, and S.A. Everett. 2007. Teaching science as investigations. Upper Saddle River, NJ: Pearson Education.

Newton, I. 1704. Opticks. London: The Warnock Library.Schmidt, H.J. 1997. Students’ misconceptions—Looking for a

pattern. Science Education 81 (2): 123–135. Steve Spangler Science. 2010. Floating bowling balls: The bowl-

ing ball science experiment that has everyone wondering. www.stevespanglerscience.com/experiment/00000067

Waugh, M. 2007. Floating boats: A scientific investigation of floating, sinking, and density. The Science Teacher 74 (5): 40–44.

April/May 2011 61

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