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You be the Judge: Density Objectives The students will: develop an understanding of density calculate density of objects collect, analyze, and interpret data solve equations collaborate with partners and share materials Standards SEP2 SEP4 SEP5 SEP6 SEP7 SEP8 5-PS1-1 MS-PS1-1 MP4 5.MD.5.b 6.EE.7 8.G.9 RI.5.4 RI.5.10 W.5.10 W.6.1 SL.5.1 RST.6-8.3 RST.6-8.7 NOTES: Background Each element, compound, atom, and substance has its own density. This physical property is a relationship between mass and volume. Density is equal to mass (g) divided by volume (ml) or D = m (g) v (ml). In chemistry, the density of objects is compared to the density of water. When an object s density is less than that of water, the object will float, but when the object s density is greater than water, the object will sink. Density can also be thought about as how tightly atoms and molecules are packed together. Inquiry Overview Students will be introduced to density by first making a visual model and exploring the relationship between size of particles and the space between them. The second activity allows students to determine density of a variety of objects. 3
Suggested Inquiry Approach o Activity #1: Work in Pairs: 1 Hour Explain to students that throughout this unit they will have several chances to observe various properties of substances. Materials Activity #1 for each Pair of Students: Dropper Bottle of Water 2 Graduated Cups Small Steel Spheres Large Steel Spheres Paper Towels Read the problem together. As the group goes through the material s list together, make sure students are acquainted with all of the items, their location, and method of distribution. Demonstrate the proper use of the water bottle. Have students take turns reading the procedure aloud, step by step. Spend time going over the data table. Ask questions to ensure students understand what data is to be collected and how the data are to be organized. Assist pairs of students as they work through the activity. NOTES: When students have had a chance to answer the questions, host a whole group discussion. Explain to students that they have been working with the concept that is called density in science. Density is very important as it affects how substances interact and react with other substances. The size of the particles has an effect on the size of the space between particles. This can translate into a variety of ideas, but the one we are focusing on is that of density. When the particles are more tightly packed, the substance is denser compared to an object that is packed more loosely. A more familiar example may be a snowball. A tightly packed snowball has a greater density than a loosely packed one. Other examples students may be able to easily relate to include less crowded and more crowded areas associated with schools, such as lunchrooms, classrooms, hallways, and busses. Have students record their data on the class data sheet. Discuss the data. Have students share their drawings. Solicit ideas for any differences, similarities, and trends. Discuss the questions from student page 12. Activity #2: o Work in Pairs: 1.5 Hours o 1 Hour to Complete Activity #2 o 30 Minutes to Discuss Class Data & Debrief 4
Have students explain to each other in their own words what density is. Next have them make two drawings: one of a less dense object and one of an object with greater density. They should label their drawings and explain the drawings to their partners first and then to entire group. NOTES: Share with the group that they will now have the opportunity to determine a more accurate density of several objects. As before in Activity #1, read through the purpose, materials, procedure, and data table together prior to beginning the activity. Students may need assistance when finding the volume of each of the solids. Write and explain each of the equations for the students to copy on their student pages. They will need these for their calculations. Materials Activity #2 Class to Share: 5 Aluminum Cubes 5 Aluminum Cylinders 5 Aluminum Rectangular Prisms 5 Steel Cubes 5 Steel Cylinders 5 Steel Rectangular Prisms Scale Each Pair of Students: Calculator Cup Paper Towels Ruler Water FORMULAS for finding VOLUME Volume of a Cube = Length x Width x Height Volume of a Rectangular Prism = Length x Width x Height Volume of a Cylinder = pi x Radius x Radius x Height Pi = 3.14 Assist groups as they work through the activity independently. When students have completed the activity, ask the following questions: Which of the blocks sunk? Which block had the greatest density? o What evidence do you have? o How do you know this? What could that mean about how its particles are packed together? Which of the blocks floated? Which block had the smallest/least density? o What evidence do you have? o How do you know this? 5
What could that mean about how its particles are packed together? Have students go back to their drawings and make any corrections they need to based on the activity and discussion. Students share and explain their drawings to the group. Debrief How would you describe density? How do you think density affects matter? Why would it be important to know the density of an object? Where are some places that you have seen the effects of density in action? Extensions Test aluminum foil to see if it will sink or float. Change the shape of the foil to test the effects of shape on density. Determine the density of other regularly shaped objects. Predict if they will sink or float and test them. 6
You be the Judge: Density Pg. 1 0f 4 Problem: How does the size of the particle affect the amount of space in a container? Materials: (Per Pair) 2 Graduated Cups Dropper Bottle of Water Smaller Steel Spheres Larger Steel Spheres Paper Towels Procedure: 1. Fill the graduated cup with smaller steel spheres until the bottom has one layer. 2. Count and record how many steel spheres covered the bottom of the container. 3. Make a drawing of your observations. 4. Slowly add drops of water one at a time to the container until the steel spheres are covered. Count the number of drops as you add the drops. Record this number on the data table. 5. Look at the cup from the side. Record any additional observations on the data table. 6. Set this cup aside. 7. Fill the other graduated cup using the larger steel spheres until the bottom has one layer. 8. Count and record how many steel spheres covered the bottom of the container. 9. Make a drawing of your observations. 10. Repeat steps 4 and 5. Remember to record the data and observations on the table. 7
You be the Judge: Density Pg. 2 0f 4 11. Answer the discussion questions. 12. Empty the water from the containers. Dry the containers and the steel spheres. Return the steel spheres to the appropriate containers. Cup Small Steel Spheres DENSITY DATA TABLE Number of Number of Steel Drops of Spheres Water Other Observations Large Steel Spheres 8
You be the Judge: Density Pg. 3 0f 4 Drawings of Small Steel Spheres Drawings of Large Steel Spheres 9
You be the Judge: Density Pg. 4 0f 4 Discussion and Conclusions: 1. What filled the spaces between the steel spheres? 2. Which cup held the most water? 3. How would you describe the relationship between the size of the steel spheres and the number of spheres that fits in the bottom of the cup? 4. How would you describe the relationship between the size of the steel spheres and the amount of water that fits in the spaces between them? 10
You be the Judge: Density Pg. 1 0f 4 Problem: How does density affect an object? Materials: (Group of 4) Aluminum Cube Aluminum Cylinder Aluminum Rectangular Prism Steel Cube Steel Cylinder Steel Rectangular Prism Ruler Calculator Cup Water Paper Towel Scale Procedure: 1. Find the mass of each block. Record this on the data table. 2. Determine the volume of each of the three shapes. Write the formula you will use. Show your work on the next page. Make sure to record the volume of each shape on the data table. Volume of a Cube Volume of a Rectangular Prism Volume of a Cylinder 3. Determine the density of each of the blocks. 4. Use your data to calculate the density. 5. Predict if each block will sink or float in water. 6. Test your predictions one block at a time. Record the results. 7. Thoroughly dry off each object. 8. Clean up following your teachers directions. 11
You be the Judge: Density Pg. 2 0f 4 VOLUME CALCULATIONS Shape Formula Shape Formula Shape Formula 12
You be the Judge: Density Pg. 3 0f 4 Equation for Density: Metal Type Mass & Shape (g) SINK or FLOAT DATA TABLE Volume (cm 3 ) Density (g/cm 3 ) Prediction Results 13
You be the Judge: Density Pg. 4 0f 4 Discussion and Conclusions: 1. What surprised you from the results? Explain your answer. 2. Explain why something was able to float. 3. Explain why something was able to sink. 4. How do you think this relates to the previous activity with the steel spheres? 14
You be the Judge: Density Group Small Steel Spheres Large Steel Spheres # Spheres Drops Water # Spheres Drops Water 1 2 3 4 5 6 7 8 9 10 Average Transparency Master 15