SINK OR FLOAT?
A LESSON ABOUT DENSITY
Lesson Activities
Teacher should attempt to run the simulation before the day of giving the lesson to make sure flash does not need to be loaded onto the computers before students access the lab.
Materials needed to assemble ahead of time-
1. Aluminum and oak density cubes (set per student group.)
2. 200 ml clear glass beakers or 6 oz. glass cups/jars (2/3 filled with water)
3. Metric scales- to measure mass of cubes (Several to be shared by groups.)
4. Recording sheets (see “Student Activities and Resources”)
Next Generation Science Connections
Foundational understanding of density also needed for MS Weather & Climate, Earth Systems and Matter for Physical Science.
Evidence Statements are from http://www.nextgenscience.org/middle-school-evidence-statements
ENGAGE
Arrange students in groups of 2, 3 or 4 (depending on the way you will want them to work on computers later in the Explore Activity.) Pairs are preferable if computer availability permits this configuration. / Students form lab-partner groups depending on the directions given by the teacher.
Teacher asks: Why do you think some objects sink and some objects float in water? What are some factors that would cause objects to sink or float? (1 min) / All individual students Think-Ink-Pair-Share to discuss their ideas about this question. (3 mins)
Teacher asks a few pairs to share their ideas. (1 min) / Student pairs are called on to share their ideas. (3 mins)
Activity 1
Teacher distributes density blocks (oak and aluminum) to student groups.
Ask Students, “Predict which block will float and which block will sink”
Ask students to discuss and write their predictions in the appropriate space provided on the Recording Sheet. (Recording sheet is provided, but students could record in their science notebook as well.) (2 mins) / Activity 1
Students pick up the blocks and compare them and predict which one will sink and which one will float?
Students write predictions in the appropriate space provided on the Recording Sheet. (3 mins)
EXPLORE
Teacher says, “You’ve all made a prediction. Now let’s look a little more closely at these blocks- Use your five senses to describe your blocks. Record at least 4 observations for each block in the appropriate area on your Recording Sheet. More than 4 may be written. (1 min) / Students will observe, discuss and record four descriptive-sensory words for each block in the appropriate area on the Recording Sheet Possible responses: shiny, dull, smooth, cube, 6-sided, metal, wood, soft, hard, heavy, light
(3 mins)
Teacher reinforces the concept of “Qualitative” data by asking, “How does defining the qualities of an object help you describe it”? (1 min) / Students share their ideas about qualitative descriptions of their objects.
(2 mins)
Teacher: “Now we are going to make some quantitative recordings of the two blocks. We are going to measure and weigh the blocks.”
“Why do you think we refer to collecting information or data about the size and weight of an object as quantitative data?”
(1 min) / Student prepare to record 2 quantitative properties (mass and volume) of data and record on their recording sheet
Student thinking & possible responses: measuring involves numbers, the measurements will be expresses in numbers, and numbers tell us a quantity.
(2 mins)
Note: In order to account for different sizes of density cubes and to avoid student confusion, we defined the length of one side of the cube as 5 cm to calculate volume. Thus, 5cm x 5cm x 5 cm= 125 cm cubed (125 cm3). This will allow a connection between the physical cubes and the virtual density cubes and highlight that three attributes of the cube are considered (length, width, height) to determine the volume.
Show students how to find cubic measurement of a cube. This represents the volume of the cube.
Students are requested to record the volume calculation in the Quantitative Table: Volume of the Lab Sheet.
(2 mins) / Student thinking & possible responses: Students have some prior knowledge that volume of an object consists of 3 dimensions: length, width, and height and that the volume in measured in cubed units (units3). For some students, this scaffolding may be needed if the concept is not yet well understood.
Students make their own calculations for the volume of the cube the Quantitative Table: Volume of the Lab Sheet.
(3 mins)
Show students how to weigh the cubes in grams on the metric scale. Suggest that only one student weigh to manage and reduce classroom traffic. The teacher observes students as they weigh and record both cubes in grams.
Ask students to record the mass for both cubes in grams Space 3 in the quantitative area of the lab sheet.
(2 mins) / Students weigh and record their findings for mass in grams in the quantitative area of the lab sheet.
Students return to their seat after obtaining the weight in grams of both cubes. They share their data with their activity partner.
(7 mins)
Teacher distributes glass beakers filled 2/3 with water to each pair of students. The water is also a connection to what the students will do in the density simulator tool of testing cubes in water.
Ask the students test their hypothesis of sink or float by placing cubes into water.
Remind students to be careful not to spill water on the computers that may be nearby.
(2 mins) / Students place blocks in beaker of water, compare their prediction and what actually happened, and record result on their recording sheet
Student thinking & possible responses: wood floats and aluminum sinks.
(2 mins)
After students have tested the cubes, guide them into understanding that the cubes have the same volume but different masses and this is related to density of the cubes. The teacher introduces density as the ratio between the mass and the volume of an object. A suggestion is not to “over-explain” the relationship between mass and volume, as students will explore this relationship using a virtual density simulator.
Teacher tells students to discuss with their partner what a ratio is.
(3 mins) / Students write the expression, mass over volume, in a ratio format to show the pattern of the relationship.
Student thinking & possible responses: Students demonstrate understanding that a ratio represents a relationship stated as a division operation.
(4 mins)
Teacher asks: Other than mass, what is the difference between these two cubes?
Remind students: The volume of the two cubes is the same, and the mass is different. Therefore, the density will be different.
(1 min) / Think-Ink- Pair-Share to come up with the answer that the density of one is greater than the other. Students record the difference between the two cubes response in their recording sheet.
Student thinking & possible responses: Students may say that even though both cubes have the same volume, the mass must be why one sinks and one floats. Students may not yet be able to say that the density of the cubes is different. (2 mins)
Explain 1- Have students write a why they think things sink or float / Many students at this point will talk about mass as the reason things sink or float.
Activity 2
Teacher instructs student to go to the density simulator tool that has been uploaded from the Internet to students’ computers:
http://phet.colorado.edu/sims/density-and-buoyancy/density_en.html
Students will be told to explore the simulator using the “Material” option on the upper left corner of the simulator and the “Custom” option in the upper-hand corner of the simulator under the “Blocks” menu.
Note: Tell students that the term “cubes” and “blocks” are interchangeable during the rest of the lesson. (2 mins) / Activity 2
Student pairs use one computer and access the PhET density simulator.
Students use the simulation tool to explore density of the listed blocks.
Students repeat back to the teacher that “blocks” and “cubes” are interchangeable terms.
(2 mins)
Teacher instructs students to test each material (in the form of cubes). Materials are Styrofoam, wood, ice, brick, and aluminum.Teacher will emphasize to students that the volume of the cubes is the same (constant) as it was in the wood and aluminum cubes.
Teacher tells students to record sinking and floating of materials as well as any relationships that they see between mass and buoyancy. Students are reminded that buoyancy refers to the ability of an object to sink or float.
Point out to students that they will record observations on their recording sheet for each material (cube) given in the simulator.
Teacher tells students that In the recording sheet, two main categories are listed (Sink and Float). Under each main category is: Material, Mass/Volume Ratio (remind that the volume will be the same) and Density. Teacher tells students to observe all numeric data in the simulator and to write it in their recording sheet. / Students use the simulator to test each material (in the form of cubes). Students understand the volume of the cubes is the same (constant).
Students record observations on their recording sheet for each material (cube). Two main categories are listed (Sink and Float). Under each main category: Material, Mass/Volume Ratio (volume will be the same) and Density.
Student thinking & possible responses: Students should note that the volume of the five (5) materials is the same, and the mass of the different materials will increase. The density will vary, however, depending on the material, and is also given as a numeric value in the simulator.
Students will record all numeric data provided (given) in the simulator for each material.
(10 mins)
Student thinking & possible responses: The objective is for students to note that as the mass of a given cube increases, so does its density. The density is given as kg/liter
(3 mins)
Explain 2:
Have students look at their data and look for and record a pattern observed / Students will notice objects with greater mass sink as previously observed.
Some students will hopefully see that objects with density less than one float and greater than one sink.
Activity 3:
Using the same PhET density simulator, have students choose the “Same Volume” option under “Blocks” in the upper right hand corner. Before proceeding to put the four blocks with the same volume in the water one at a time, have students first make predictions based on the sinking or floating of the red, green, yellow, and blue cube. That is, which blocks will sink and which will float.
Note: Students should observe that the cubes have the same volume but have different masses in kilograms (kg), which is noted on each block.
Frontload students with the fact that the volume is the same for all 4 color blocks. Teacher guides students into thinking what the volume of all four blocks could be.
(4 mins) / Activity 3:
Students use the PhET density simulator to choose the “Same Volume” option.
Students first make predictions before putting the blocks one at a time into the water,
Students record their predictions as to sink or float on their recording sheet.
Student thinking & possible responses: Students are not mathematically calculating the volume but are determining the relationship between the mass of a given cube and its ability to sink or float (i.e., buoyancy) Students will notice that all four color blocks (cubes) are exactly the same “size” which refers to having the same volume. Students will also notice that they each have a different mass.
Students will think about what numeric value the volume could be if the volume is the same for all of the cubes.
(13 mins)
Note: The objective is for students to think about the density of each block based on whether it sinks or floats. They should think about the previous activity where Density = mass/volume. Therefore, if the blocks all have the same volume but they vary in their mass, then the greater the mass, the greater the density. Another way for students to look at this concept is that if the mass of a cube is greater than its volume, the cube will sink and if the mass of a cube is less than its volume, the cube will float. This concept may not be readily understood unless students remember that the volume is held constant in this activity. The teacher may want to make some brief comments about these ideas if he/she deems it appropriate for his/her students. Bring students to a point where they consider what the volume could be numerically (it can be any value as long as the value is the same for all of the cubes.)
EXPLAIN
Teacher Does (1 min) / Student Does (4 mins)Teacher directs students to think about a
conclusion as to why the cubes in the activities sank or floated. Allow students to think-ink-pair-share.
Teacher directs students to make a general statement about the relationships between mass, volume and density. In other words, why do things sink or float? Request students to write this relationship on their recording sheet. / Student pairs think-ink-pair-share their conclusion regarding why the aluminum sunk and why the wood floated.
Student pairs gather their ideas and create a general statement about the relationships between mass, volume and density to answer the question, why do things sink or float? Students write this relationship on their recording sheet and share with their partner.
Students then share their conclusion with the whole class.
EXTEND