LESSON 4: Buoyant Butter ESTIMATED TIME Setup: 5 minutes Procedure: 5 10 minutes

LESSON 4: Buoyant Butter ESTIMATED TIME Setup: 5 minutes Procedure: 5 10 minutes DESCRIPTION Calculate the density of a stick of butter to determine if it will sink or float in water. OBJECTIVE This lesson teaches students about density, how to calculate it, and how it is related to determining whether an object will sink or float in a certain liquid. Students will measure sticks of butter or margarine to determine whether they will sink or float in water. The lesson can be simplified to reinforce the importance of measurement in a scientific experiment. CONTENT TOPICS Scientific inquiry; measurement; properties of matter (density) MATERIALS o Stick of butter or margarine (with the wrapper on) o Metric ruler o Large bowl or container Always remember to use the appropriate safety equipment when conducting your experiment. Refer to the Safety First section in the Resource Guide on pages 421 423 for more detailed information about safety in the classroom. Jump ahead to page 58 to view the Experimental Procedure. NATIONAL SCIENCE EDUCATION STANDARDS SUBJECT MATTER This lesson applies both Dimension 1: Scientific and Engineering Practices and Dimension 2: Crosscutting Concepts from A Framework for K 12 Science Education, established as a guide for the updated National Science Education Standards. In addition, this lesson covers the following Disciplinary Core Ideas from that framework: PS1.A: Structure and Properties of Matter PS2.A: Forces and Motion ETS2.A: Interdependence of Science, Engineering, and Technology (see Analysis & Conclusion) ETS2.B: Influence of Engineering, Technology, and Science on Society and the Natural World (see Analysis & Conclusion) OBSERVATION & RESEARCH BACKGROUND Mass and volume are common units of measure. Mass is a measure of the amount of matter in a substance. (It s the amount of stuff in a substance.) Volume is the amount of space an object occupies. Density is an important concept in chemistry that is defined as the mass of an object per unit volume. Density is a physical property of matter that describes how closely packed together the atoms or molecules of a substance are. The formula used to calculate density is d = m/v, where d is the density, m is the mass of the object, and v is the volume of the object. Scientists use density in different ways. They use it to identify unknown substances and to separate different liquids. In this experiment, students determine the density of an object and compare it to the density of water. The approximate density of liquid water is 1.0 gram per milliliter (g/ml). This means that one milliliter of water will have a mass of one gram; thus, it will weigh one gram on the earth. In general, a substance that is less dense than water will rest on top of the water, and a substance that is denser than water will sink. Therefore, a copper coin, which has a density of 8.96 g/cm 3 would You Be The LESSON Chemist 1: Activity Goofy Guides Putty page 55 55

LESSON 4: Buoyant Butter sink in water. On the other hand, if we have a 10-gram piece of wood with a volume of 20 milliliters, we would first calculate the density of the wood. Using the equation, we know that the density of the wood is 0.5 g/ml. Because this number is less than the density of water (1.0 g/ml), the wood will float. You can also determine whether the wood will float using another method. Since we know the object weighs 10 grams and the volume is 20 milliliters, we can then determine how much 20 milliliters of water weighs. The answer (using the density equation) is 20 grams, which is more than the piece of wood. Therefore, again, we know that the wood will float. Density, however, is not the only consideration. Think about a ship made of steel. Although steel has a density greater than water, the shape of the boat spreads the weight of the steel over a larger space. In addition, some of that space is filled with air, which is much less dense than water. Therefore, whether an object sinks or floats also has to do with displacement. Displacement occurs when one substance takes the place of another. When an object is placed in water, it will displace some of the water. (Think about sitting in a bathtub. When you sit down, the water will rise, as your body takes the place of some of the water.) In general, if an object weighs more than the water it displaces, the object will sink. If an object weighs less than the water it displaces, it will float. Buoyancy is the upward force that a fluid exerts on an object that enables the object to float. The buoyant force on an object is equal to the weight of the fluid displaced by the object. FORMULAS & EQUATIONS Certain laboratory equipment can be used to gather different measurements. The mass of an object can be determined by using a balance. The volume of a liquid can be easily determined by pouring the liquid into a graduated cylinder. For solid objects, measuring volume takes a little more effort. You can calculate the volume of rectangular solids with the following equation: CONNECT TO THE YOU BE THE CHEMIST CHALLENGE For additional background information, please review CEF s Challenge study materials online at http://www.chemed.org/ybtc/challenge/study.aspx. Additional information on measurement and types of physical measurements can be found in the Measurement section of CEF s Passport to Science Exploration: The Core of Chemistry. Additional information on properties of matter can be found in the Classification of Matter section of CEF s Passport to Science Exploration: The Core of Chemistry. Additional information on displacement can be found in the Laboratory Equipment section of CEF s Passport to Science Exploration: The Core of Chemistry. The volume of a solid is therefore measured in cubic centimeters (or cubic meters). For solids with an irregular shape, you can use a displacement method. Once the mass and volume of an object have been determined, the density of that object can be calculated. Use the following equation: d = m/v. Density is measured in grams per milliliter or grams per cubic centimeters. One cubic centimeter (cm 3 or cc) is equal to one milliliter (ml). HYPOTHESIS udensity can be calculated using the mass and volume of an object. If the average density of an object is less than the average density of water, it will float. v = l w h where v is the volume, l is the length of the object, w is the width of the object, and h is the height of the object. You Be The Chemist Activity Guide page 56

LESSON 4: Buoyant Butter DIFFERENTIATION IN THE CLASSROOM LOWER GRADE LEVELS/BEGINNERS DESCRIPTION Practice performing different measurements to reinforce the importance of measurement and explain the difference between accuracy and precision. Students will calculate the mass, volume, and density of different sized pieces of butter. OBJECTIVE This lesson reinforces the importance of measurement and allows students to practice measuring mass, volume, and density. OBSERVATION & RESEARCH Measurement is perhaps one of the most fundamental concepts in science. It is the process of determining the ratio of a physical quantity, such as length or a mass, to a unit of measurement. Without the ability to measure, it would be difficult for scientists to conduct experiments or form theories. Not only is measurement important in science, but it is also essential in industry, farming, engineering, construction, manufacturing, commerce, and numerous other occupations and activities. A good example of measurement is using a ruler to find the length of an object. The object is whatever you are measuring, the property you are trying to determine is the object s length, and the standard you are comparing the object s length to is the ruler. Scientists have two goals when they take measurements. They want their measurements to be accurate by getting as close as possible to the true measurement of something. They also want their measurements to be precise so that they can take the same measurement and get the same result over and over. You should strive to achieve accuracy and precision in your measurements. Measurement is never 100% accurate, so the true value of a measurement is never exactly known. This uncertainty is a result of error, a concept which is associated with measuring, because measurement is always a comparison to a standard. Manually measuring something always involves uncertainty because it is based on judgment. If two people use a ruler to measure how tall a plant is, it may look like 20 cm to one person and 18 cm to the other. To increase the accuracy of a measurement, therefore reducing error, an object should always be measured more than once. Taking multiple measurements and then determining the average measurement increases the likelihood that you have the exact measurement. There are several properties of objects that scientists need to measure, but the most useful and common properties are length and mass. Length is a measure of how long an object is, and mass is a measure of how much matter is in an object. Mass and length are base units, meaning that they are independent of all other units. Most units of measure, such as volume and density, are derived or calculated from base units. For example, density is derived from the base measurement units of mass and length. Density is an important concept in chemistry, defined as the mass of an object per unit volume. Density is a physical property of matter that describes how closely packed together the atoms of an element or the molecules of a compound are. The formula used to calculate density is d = m/v, where d is the density, m is the mass of the object, and v is the volume of the object. CONNECT TO THE YOU BE THE CHEMIST CHALLENGE For additional background information, please review CEF s Challenge study materials online at http://www.chemed.org/ybtc/challenge/study.aspx. Additional information on measurement can be found in the Measurement section of CEF s Passport to Science Exploration: The Core of Chemistry. Additional information on measuring mass and volume can be found in the Laboratory Equipment section of CEF s Passport to Science Exploration: The Core of Chemistry. Additional information on density can be found in the Classification of Matter section of CEF s Passport to Science Exploration: The Core of Chemistry. You Be The Chemist Activity Guide page 57

LESSON 4: Buoyant Butter DIFFERENTIATION IN THE CLASSROOM HIGHER GRADE LEVELS/ADVANCED STUDENTS Perform the experiment as described below, but explore the concept of density further. Have students perform different measurements and calculate the density of various objects. Discuss density as it relates to solids, liquids, and gases. Can liquids float on top of one another? See the Modifications/Extensions section for other ideas to reinforce the concept of density. Another option is to discuss buoyancy in more detail, as well as other forces, such as gravity, friction, and nuclear forces. Explore the differences between those forces. EXPERIMENTATION As the students perform the experiment, challenge them to identify the independent, dependent, and controlled variables, as well as whether there is a control setup for the experiment. (Hint: If you change the volume of the stick of butter, will it act the same way in water?) Review the information in the Scientific Inquiry section on pages 14 16 to discuss variables. EXPERIMENTAL PROCEDURE Before the experiment, ask the students if the stick of butter will float or sink in water. Ask them if they know how to figure this out without testing it in water. 1. Determine the mass of the butter or margarine in the stick. This amount (in grams) is printed on the wrapper of the butter. You can also weigh the butter on a balance to find the mass. 2. To determine how much space the butter takes up (volume), measure the length, width, and height of the stick of butter in centimeters (cm). 3. Multiply length width height, and record that number in cm 3, which is equal to a milliliter (ml). 4. To determine the approximate density of your stick of butter, divide the mass of the butter (in grams) by its volume (in cm 3 ). 5. Now compare your calculated density of the butter to that of water (1 g/ml), and determine whether the object will sink or float. 6. Fill the bowl or container with water, and place the stick of butter in the water to observe what happens. It is best to use a frozen stick of butter. DATA COLLECTION Have students record data in their science notebooks or on the following activity sheet. What are the measurements for length, width, and height of the stick of butter? What is the mass of the stick of butter? You can use the table provided in the activity sheet (or a similar one of your own) for students to record their data. NOTES You Be The Chemist Activity Guide page 58

ANALYSIS & CONCLUSION LESSON 4: Buoyant Butter Use the questions from the activity sheet or your own questions to discuss the experimental data. Ask students to determine whether they should accept or reject their hypotheses. Review the information in the Scientific Inquiry section on pages 14 16 to discuss valid and invalid hypotheses. ASSESSMENT/GOALS Upon completion of this lesson, students should be able to Apply a scientific inquiry process and perform an experiment. Understand the importance of taking careful measurements. Understand density, displacement, and buoyancy as they relate to whether an object will sink or float in a liquid. Explain the concept of density and calculate the density of an object if given the mass and volume. Understand the importance of accuracy and precision to measurement (see Differentiation in the Classroom). MODIFICATIONS/EXTENSIONS Modifications and extensions provide alternative methods for performing the lesson or similar lessons. They also introduce ways to expand on the content topics presented and think beyond those topics. Use the following examples, or have a discussion to generate other ideas as a class. Try using sticks of butter at different temperatures. Ask the students if they think a frozen stick of butter and a room-temperature stick of butter will act the same when placed in water. Then, place each in water to see what happens. Try different objects, and ask the students if the objects will sink or float. Ask them what that means about the density of the object in relation to the K-4 5-8 water. You can also discuss the differences between salt water and freshwater. Ask them to think about whether it is easier to float in the ocean or a freshwater pool. Because salt water is denser than freshwater, people can float much easier in the ocean. Explain the concept of density using a visual. For example, use mini-marshmallows in a clear box to show how mass can change in a given volume. See Lesson 12: Density Totem for another lesson on density. See Lesson 19: Liquid Rainbow for a more complex density lesson. REAL-WORLD APPLICATIONS Challenge the students by asking them how huge boats made of metal can float. Then, explain that the massive weight of the boat is spread out over a large area. Thus it has a large volume, making it possible to float in water. The concepts of density and buoyancy are vital to the development of large ships, such as aircraft carriers, cargo ships, and cruise ships. COMMUNICATION Discuss the results as a class and review the activity sheet. Review the information in the Scientific Inquiry section on pages 14 16 to discuss the importance of communication to scientific progress. Fun Fact The Dead Sea, which is located in the Middle East, has a very high concentration of salt. Its density is so great that anyone can float, almost lie, in the water. You Be The Chemist Activity Guide page 59

OBSERVE & RESEARCH 1. Write down the materials you observe. 2. Predict how these materials may be used. 3. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an image of the example. Term Definition Example (write or add image) Mass Volume Density Displacement 4. Consider what will happen when the stick of butter is placed in water and why. uwrite your hypothesis. You Be The Chemist Activity Guide page 60

PERFORM YOUR EXPERIMENT 1. Determine the mass of the stick of butter. This amount (in grams) is printed on the wrapper or can be found by placing the stick of butter on a balance. 2. Measure the length, width, and height of the stick of butter in centimeters (cm) to determine the volume. 3. Multiply the length, width, and height (length width height). Record that number in cm 3. This amount is the volume. 4. Determine the approximate density of your stick of butter by dividing its mass by its volume. 1 cm 3 = 1 ml. Use this formula to convert your units from g/cm 3 to g/ml. 5. Compare your calculated density of the butter to the density of water (1 g/ml). Do you think the butter will sink or float? 6. Fill the bowl with water, and place the stick of butter in the water. Observe what happens. ANALYZE & CONCLUDE 1. Record your measurements and calculations in the following table. Mass of Butter (g) Length (cm) Width (cm) Height (cm) Volume (cm 3 ) Density of Butter (g/cm 3 ) Density of Water (g/ml) You Be The Chemist Activity Guides page 61

2. What is the formula for density? What is the unit of measurement for density? 3. Based on your calculation, is the density of the butter greater or less than the density of water? 4. Do you think the butter will sink or float? Why? 5. If you place the stick of butter in salt water, do you think it will sink or float? Why? 6. Is your hypothesis valid? Why or why not? If not, what would be your next steps? You Be The Chemist Activity Guide page 62

SHARE YOUR KNOWLEDGE 1. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an image of the example. Term Definition Example (write or add image) Measurement Accuracy Precision 2. List some objects that you think have a density greater than water. 3. List some objects that you think have a density less than water. 4. If you cut the stick of butter in half, will its density change? Why or why not? You Be The Chemist Activity Guides page 63

ANSWER KEY: Below are suggested answers. Other answers may also be acceptable. OBSERVE & RESEARCH 1. Write down the materials you observe. Stick of butter/margarine, metric ruler, large bowl, water 2. Predict how these materials may be used. The butter may be used for cooking. The ruler may be used to take measurements. The bowl may be used to hold water or other materials. These materials may be used to identify and compare the physical properties of butter and water. 3. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an image of the example. Term Definition Example (write or add image) Mass A measure of the amount of matter in a substance. Volume A physical property that measures the amount of space a substance occupies. Density A physical property of matter that describes how closely packed together the atoms of an element or the molecules of a compound are; the amount of matter per unit of volume (d = m/v). Displacement The act of moving something out of its original position or of one substance taking the place of another. 4. Consider what will happen when the stick of butter is placed in water and why. uwrite your hypothesis. Density can be calculated using the mass and volume of an object. If an object is denser than the water it displaces, it will sink. If an object is less dense than the water it displaces, it will float. You Be The Chemist Activity Guide page 64

ANSWER KEY: Below are suggested answers. Other answers may also be acceptable. PERFORM YOUR EXPERIMENT 1. Determine the mass of the stick of butter. This amount (in grams) is printed on the wrapper or can be found by placing the stick of butter on a balance. 2. Measure the length, width, and height of the stick of butter in centimeters (cm) to determine the volume. 3. Multiply the length, width, and height (length width height). Record that number in cm 3. This amount is the volume. 4. Determine the approximate density of your stick of butter by dividing its mass by its volume. 1 cm 3 = 1 ml. Use this formula to convert your units from g/cm 3 to g/ml. 5. Compare your calculated density of the butter to the density of water (1 g/ml). Do you think the butter will sink or float? 6. Fill the bowl with water, and place the stick of butter in the water. Observe what happens. ANALYZE & CONCLUDE 1. Record your measurements and calculations in the following table. Mass of Butter (g) Answers will vary Length (cm) Answers will vary Width (cm) Answers will vary Height (cm) Answers will vary Volume (cm 3 ) Answers will vary Density of Butter (g/cm 3 ) Answers will vary Density of Water (g/ml) 1 g/ml You Be The Chemist Activity Guide page 65

ANSWER KEY: Below are suggested answers. Other answers may also be acceptable. 2. What is the formula for density? What is the unit of measurement for density? The formula for density is d = m/v. Density is measured in grams per cubic centimeter (g/cm 3 ) or grams per milliliter (g/ml). 3. Based on your calculation, is the density of the butter greater or less than the density of water? The density of butter is less than the density of water. 4. Do you think the butter will sink or float? Why? Because the density of butter is less than the density of water, the butter will float in the water. 5. If you place the stick of butter in salt water, do you think it will sink or float? Why? The stick of butter will float in the salt water. The addition of salt to water adds mass to the water. Since the formula for density is d = m/v, the density of the water increases. Thus, the butter is even less dense than the salt water. 6. Is your hypothesis valid? Why or why not? If not, what would be your next steps? Answer 1: Valid because the data support my hypothesis. Answer 2: Invalid because the data do not support my hypothesis. I would reject my hypothesis and could form a new one, such as You Be The Chemist Activity Guide page 66

ANSWER KEY Below are suggested answers. Other answers may also be acceptable. SHARE YOUR KNOWLEDGE BEGINNERS Have students complete this section if you used the beginners differentiation information, or challenge them to find the answers to these questions at home and discuss how these terms relate to the experiment in class the next day. 1. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an image of the example. Term Definition Example (write or add image) Measurement A technique in which properties of a substance are determined by comparing it to some sort of standard. Accuracy The closeness of a given measurement to the actual (true) value for that quantity of substance; to measure a quantity as close as possible to the true measurement (true value) of that quantity. Precision The degree to which repeated measurements under unchanged conditions show the same results. 2. List some objects that you think have a density greater than water. An anchor, a coin, and a dumbbell are objects that have a greater density than water. They will sink in water. 3. List some objects that you think have a density less than water. An apple, a cork, and a beach ball are objects that have a density less than water. They will float in water. 4. If you cut the stick of butter in half, will its density change? Why or why not? No, if you cut the stick of butter in half, both the mass and the volume of the butter change. The mass will be half of what it was before. The volume will also be half of what it was before. Since the density fomula is d= m/v, the density will remain the same. You Be The Chemist Activity Guide page 67