Student Exploration Density Laboratory

Name: Date: October 1, 2021 Student Exploration: Density Laboratory Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: buoyancy, density, graduated cylinder, mass, matter, scale, volumePrior Knowledge Questions 1. Of the objects below, circle ( to use the drawing tool. ) the ones you think would float in water. Click on the image and select EDIT 2. Why do some objects float, while others sink? The cruise ship, Saturn and the beach ball would all float in water. Objects that are less dense than water will float. The Density Laboratory allows you to measure a variety of objects, then drop them in water (or other liquid) to see if they sink or float. 1. An object’s mass is the amount of matter it contains. Mass can be measured with a calibrated scale like the one shown in the Gizmo. Drag the first object onto the Scale. (This is object 1.) What is the mass of object 1? 19.5 g 2. An object’s volume is the amount of space it takes up. The volume of an irregular object can be measured by how much water it displaces in a graduated cylinder. A. What is the initial volume of water in the cylinder? 400.0 mL B. Place object 1 into the cylinder. What is the volume in the cylinder now? 414.2 mL C. What is the volume of the object? 14.2 cm3 Note: While milliliters (mL) are used to measure liquid volumes, the equivalent unit cubic centimeters (cm3) are used for solids. Therefore, write the volume of object 1 in cm3. Activity A: Float or sink? ● Drag object 1 back to the shelf. ● Check that Liquid density is set to 1.0 g/mL. Question: How can you predict whether an object will float or sink? 1. Observe: Experiment with the different objects in the Gizmo. Observe the mass and volume each object, then drag it into the Beaker of liquid to see if it floats or sinks. (Notice a pin holds objects in the graduated cylinder, whether they sink or float.) Try to determine what the floating objects have in common and what the sinking objects have in common. 2. Form hypothesis: Compare the floating objects, then do the same for the sinking objects. A. What do the floating objects have in common? Have smaller mass relative to their volume. B. What do sinking objects have in common? Have a larger mass relative to their volume. 3. Collect data: Measure the mass and volume of objects 1 through 12, and record whether they float or sink in the table below. Leave the last column blank for now. Object Mass (g) Volume (cm3) 1 19.5 14.2 Sink 2 11.1 9.7 Floats 1.1 3 4.3 5.6 Floats 0.77 4 134.8 7.8 Sinks 17.3 5 3.9 3.5 Sinks 1.1 6 78.7 29.2 Sinks 2.70 7 2.3 20.8 Floats 0.1 8 24.4 25.7 Floats 0.95 9 99.6 43.9 Sinks 2.27 10 42.1 60.8 Floats 0.69 11 65.5 41.2 Sinks 1.59 12 104.3 114.1 Floats 0.91 Float or sink? Density g/cm3 1.34 4. Analyze: Look carefully for patterns in your data. A. Does mass alone determine whether an object will float or sink? Explain: No. It is a combination of mass relative to volume. B. Does volume alone determine whether an object will float or sink? Explain: No. An object's volume relative to its mass determines whether or not it floats. C. Compare the mass and volume of each object. What is true of the mass and volume of all the floating objects? For all the floating objects the volume is greater than the mass. D. What is true of the mass and volume of all the sinking objects? When the mass is greater than the volume. 5. Calculate: The density of an object is its mass per unit of volume. Dense objects feel very heavy for their size, while objects with low density feel very light for their size. To calculate density, divide the mass by volume: D = m/V. If mass is measured in grams and volume in cubic centimeters, the unit of density is grams per cubic centimeter (g/cm3). Calculate the density of each object, and record the answers in the last column of your data table. Label this column “Density (g/cm3).” 6. Analyze: Compare the density of each object to the density of the liquid, 1.0 g/mL. This is the density of water. A. What do you notice about the density of the floating objects? The density of the floating objects is less than 1. B. What do you notice about the density of the sinking objects? The density of the sinking objects is greater than 1. 7. Draw conclusions: If you know the mass and volume of an object, how can you predict whether it will float or sink in water? If the mass is less than the volume the object will likely float. If the mass is greater than the volume, the object will likely sink. Activity B: ● Drag all the objects back onto the shelf. ● Check that the Liquid density is still 1.0 g/mL. Liquid density Question: How does liquid density affect whether objects float or sink? 1. Observe: Place object 1 into the Beaker of liquid. Slowly move the Liquid density slider back and forth. What do you notice? As the liquid density increases the object floats to the surface. 2. Form a hypothesis: Buoyancy is the tendency to float. How do you think the liquid density affects the buoyancy of objects placed in the liquid? If the liquid density is greater than the density of the object, then the object will float. 3. Predict: In the table below, write the density of each object. Then predict whether the object will float or sink in each of the fluids. Write “Float” or “Sink” in each empty box of the table. Object Object density Liquid density 0.5 g/mL 1.0 g/mL 2.0 g/mL 1 1.34 Sink Sink Float 2 1.1 Sink Sink Float 3 0.77 Sink Float Float 4 17.3 Sink Sink Sink 5 1.1 Sink Sink Float 4. Test: Test your predictions using the Gizmo. Place a checkmark (\/) next to each correct prediction, and an “X” next to each incorrect prediction. 5. Draw conclusions: What is the relationship between the object density, the liquid density, and the tendency of the object to float? If the density of the object is greater than the liquid density it will sink. If the density of the object is less than the density of the liquid then it will float. Extension: King Hieron’s crown ● Drag all the objects back onto the shelf. ● Set the Liquid density to 1.0 g/mL. Introduction: In the third century B.C., King Hieron of Syracuse asked the famous mathematician Archimedes to determine if his crown was made of pure gold. This was a puzzling problem for Archimedes—he knew how to measure the weight of the crown, but how could he measure the volume? Archimedes solved the problem when he got into his bath and noticed the water spilling over the sides of the tub. He realized that the volume of the displaced water must be equal to the volume of the object placed into the water. Archimedes was so excited by his discovery that he jumped out of the bath and ran through the streets shouting “Eureka!” Question: How can you tell if a crown is made of solid gold? 1. Think about it: Gold is one of the densest substances known, with a density of 19.3 g/cm3. If the gold in the crown was mixed with a less-valuable metal like bronze or copper, how would that affect its density? It would make the gold less dense. 2. Observe: Drag each of the crowns into the liquid. Based on what you see, which crown do you think is densest? Explain why you think so. Crown B is denser because it sinks faster. 3. Measure: Find the mass, volume, and density of each of the three crowns. Mass (g) Volume (cm3) A 325.2 62.5 5.20 B 1264.2 65.5 19.3 C 306.0 61.6 4.97 Crown Density (g/cm3) 4. Draw conclusions: Which of the three crowns was made of gold? Explain: Crown B is made of gold because it’s density is 19.3g/cm 3 , which is the density of gold.