9-11 years Science Content: Physical Science Target Concepts/Skills: Density and Bouyancy Target Age group: 9-11 years Duration of activity: 3 hours Summary: In this activity children inquire about why some objects float and others do not, relating this phenomenon to the overall density of the body. Situations presented include high-mass objects that can float, like a large ship of iron, but simultaneously low-mass objects unable to float, like a small iron nail (experiment 1). In other situations presented there are large and small objects and some of each can float while others cannot (experiment 2). The inquiry leads children to learn about the principal property which determines whether or not a body floats is its density that is calculated dividing the weight of the body by the volume it occupies (experiment 3 and 4). Objective: By the end of the activity children should be able to: Indicate that there is no direct relationship between the buoyancy of an object and its mass; Indicate that there is no direct relationship between the buoyancy of an object and its volume; Determine the ratio between the mass and volume of different objects. Verify that the buoyancy of the object depends on its density and on the liquid s density. Resources: Tank with water. Several objects with different masses and sizes. Kitchen scale. Three Legos boxes with different sizes and masses Graduated ruler Large beaker of 1000 ml. Graduated cylinder of 500 ml. Rubber balloon. Water, Icebergs Authors: Mário Rui da Cunha Pereira, Hands on Science The content of the present document only reflects the author s views and the European Union is not liable for any use that may be made of the information therein.
Lesson plan (with inclusion of teacher notes) Description of activity The teacher divides the children into groups of three, asking them to bring from home objects of different sizes and weights that can get wet and some float while others sink. Experiment 1: Floating - Light or heavy objects Provide to each group a tank with water and a scales. Three objects are chosen for the experiment. After weighing pose the question: which ones do you think will float and which ones will sink? Ask the children to place the objects in the tank with water. Get them to record the behaviour of each object and discuss the differences from what they had predicted. Experiment 2: Floating - Large or small objects Using again three of the objects collected at home of different volumes, began by questioning the students about which bodies they think will float. The objects are then placed in the tank filled with water and the differences between the size of the bodies and the fact that some float while others don t is discussed. Children are asked to give examples of large and small objects with different floating behaviours. Experiment 3: Floating - Density Now each group will have three closed boxes filled with Legos, having different sizes and masses. Begin by measuring the dimensions of each box and its weight. The volume of each box is determined. Then measure the volume of water equal to each of the boxes and its weight is recorded. Students are asked about which of the boxes they think will float and which will sink. The boxes are placed one by one in water and record which float and which sink. For each case the ratio between mass and volume, density, is calculated and the same calculation is made for the different water volumes. Students are questioned if with the values obtained they could predict which ones would float. Experiment 4: Quiz - Will they float? Students are challenged to test with one of the objects collected from home if it will float or sink, using the previous conclusions made. This requires a tank, a beaker which fits the object and a graduated cylinder. They start by measuring the mass of the object, using the scale, and the volume, by the volume of the spilled liquid from the filled beaker to the tank when the object is completely submerged. Compare the density of the body with the density of water and verify that its behaviour is in agreement with expectations. Students are also asked what would happen if an object has a density equal to water. Fill a rubber balloon with water and place it in the water. Students comment what they observe 1. Engage (Forming hypotheses) Stimulus: Children are asked what happens when an object is placed in water. Pose the questions: Why do some bodies float and others sink? Does the mass of the body determine if a body floats? Does the volume of a body determine if a body floats? Could it be another property of the body? Can we predict if a body floats or sinks based on its properties? 2. Inquiry (Designing and running experiments and observations) Investigation: How can we find out what makes a body float or sink? In order to answer the questions previously set ask the children to plan experiments to test the different hypotheses using bodies with: 1. Different mass; 2. Different volume. The teacher explains how to use a table to organize the collected data. The children conduct a new experiment to determine a property of the bodies that relates its mass and volume. 1. They measure mass and volume of different bodies; 2. They measure mass and volume for different water samples. Finally ask the children to plan an experiment to discover if a body should float or sink.
3. Evaluation (Evaluating evidence) Evaluation, explanation of findings Results are presented to all class by group leaders. Using the collected data, students must come to the evidence that: the mass or the volume of a body, alone, does it determine if a body floats or sinks; the ratio between the mass and the volume is constant for the water; only bodies with density lower than the water will float in water; and if they know the overall density of a body they can predict if it will float or sink when put in the water. Extended thinking: What happens if a body has the same density as water is dropped in water? What happens when we transform the liquid water to ice? And what happens if instead of water we have another liquid, like oil?
Teacher Notes Experiment 1: Floating - Light or heavy objects To each group is delivered a tank with water and a scale. Three objects are chosen for the experiment. After weighing pose the question: which ones the students think will float and which ones they think will sink. The objects are then placed in the tank with water. Record the behaviour of each body and discuss the differences from what was anticipated. Experiment 2: Floating - Large or small objects Using again three of the objects collected at home with different volumes, we began by questioning the students about which bodies they think will float. The objects are then placed in the tank filled with water and the differences between the size of the bodies and the fact that same float while others don t is discussed. Children are asked to give examples of large and small objects with different floating behaviours. Experiment 3: Floating - Density Now each group will have three closed boxes made with Legos, with different sizes and masses. Begin by measuring the dimensions of each box and its weight. The volume of each box is determined. Then measure a volume of water equal to each of the boxes and its weight is recorded. Students are asked about which of the boxes they think will float and which will sink. The boxes are placed one by one in water and record which float and which sink. For each case the ratio between mass and volume, density, is calculated and the same calculation is made for the different water volumes. Students are questioned if with the values obtained they could predict which ones would float. Experiment 4: Quiz - Will they float? Students are challenged to test with one of the objects collected from home the previous conclusion. This requires a tank, a beaker which fits the object and a graduated cylinder. They start by measuring the mass of the object, using the scale, and the volume, by the volume of the spilled liquid from the filled beaker to the tank when the object is completely submerged. Compare the density of the body with the density of water and verify that its behaviour is in agreement with expectations. Students are also asked what would happen if an object have a density equal to water. Fill a rubber balloon with water and place it in the water. Students comment what they observe.
Experiment 1: Floating - Light or Heavy Objects Topic: Buoyancy and Mass Concept: The body mass alone does not determine if it floats or sinks. Problem: What determines whether a body floats the sink? Introduction You have probably already observed the behaviour of various objects when placed in water, some float while others sink. If we try to land a stone in the water of a lake, no matter how careful we are, it will immediately sink. But if we do the same with a piece of wood, no matter how high we let him fall, it insists on keeping close to the surface, floating. If we reduce the size of the stone it will continue to sink while the wood will continue to fluctuate even if it has the size of a tree. What properties determine whether an object floats or sinks? Material Several objects collected by the students with different masses and densities. A large tank with water. A kitchen scale. Experience Implementation 1. Children are divided into groups of three. Each group is given a tank with water. 2. The children are asked to place three of the collected objects, one at a time, in the balance and record its mass. 3. The objects are place in the tank with water and children record which ones float and which sink. Experience Guidance Previously the teacher should ask students to collect various objects for the experiments with different masses and densities, taking care to state its maximum size according to the tubs and selecting objects that can get wet. Before the beginning, the teacher should help to select objects for this experiment with similar dimensions and in which there is at least one that floats and one that sinks. After all objects have been weighed the teacher can ask: - Which objects you think will float? Throughout this experience the students should be able to realize that: - There are massive bodies that float and while others sink and the same happen with the lightest. - It is not the body mass alone that determines whether or not an object floats.
Student Sheet 1. Preparing the experience Which bodies are able to float? Does the mass of a body determine whether it floats or sinks? What will you need? 1. A large tank with water. 2. Several objects with different masses. 3. A kitchen scale. What do we want to discover from this experience When we place a light object in water it: Floats. Sinks. Depends on the size. When we place an heavy object in water it: Floats. Sinks. Depends on the size. Why do you think that? 2. Now let s make the experience How do we do it? 1. Place the water tank carefully on the table. 2. Using the kitchen scale, weight each of the objects selected for the experiment. 3. Place all objects, one by one, in the water. 4. Register which objects float and which sink. What do we observe? 1 When we place the objects in the water: They all sink. They all float. Some sink while others float. 2. When comparing with each body s mass we can conclude that: The heaviest sink. The lightest sink. Do not depend only on the mass (some lighter sink and some heavier float). 3. After the experience What have you learned from this experience? (you can tick more than one answer) All heavy bodies sink. The ability of a body to float does not depend only on its mass. For a body to float is not enough to be lightweight. All light bodies float. Go back and check if your answers were correct. They were all right They were all wrong Some were right and some were wrong
Experience 3: Floating - Density Teacher s Notes Topic: Buoyancy and Density Concept: For an object to float the ratio between its mass and the volume it occupies should be less than the one of the liquid. Problem: What determines whether a body floats the sink? Introduction You have probably already observed the behaviour of various objects when placed in water, some float while others sink. If we try to land a stone in the water of a lake, no matter how careful we are, it will immediately sink. But if we do the same with a piece of wood, no matter how high we let him fall, it insists on keeping close to the surface, floating. If we reduce the size of the stone it will continue to sink while the wood will continue to fluctuate even if it has the size of a tree. What properties determine whether an object floats or sinks? Materials Three boxes, built with Legos with different sizes and masses. A large tank with water. A kitchen scale A graduated ruler A large beaker of 1000 ml. A 500 ml graduated cylinder. Experience Implementation 1. Each group will have a set of three boxes and begin by determining their size by measuring the length of its edges. Record values and calculate the volume of each box. 2. Using the kitchen scale, weight each box and register the obtained values. 3. Next, weight in the graduated cylinder volumes of water equal to each box. 4. The boxes are placed in the water tank and students observe and register its behaviour. 5. Students try different mathematical relations between the mass and the volume for each box and for the different water volumes in order to find the appropriated property. 6. Students compare the obtained values for the boxes densities with what they observed in terms of its ability to float. Experience Guidance The teacher can use this experience to instruct the students about the construction of tables as a way to record data (in this case, on one column the list of boxes followed by their mass, volume, mass of an equal volume of water, prediction of whether they float or not, what they observed when put in water and the calculations of the possible relations between the two quantities). After the measuring and weighing phase of the boxes the teacher should ask: How will each box behave? Why? When calculating the mathematical relation between mas and volume teachers should stress the fact that they search for a relation that should always give the same value for the same material highlighting the character of a material property. At the end students should be questioned about their ability to predict if a body will float or not without loading it into the water. Throughout this experience the students should be able to realize that: - The density is a property of materials and is defined as the ratio between the mass of a body and its volume. - It s the overall density of a body that determines if, when putted in water, it will float or sink.
Student Sheet 1. Preparing the experience Which bodies are able to float? What property of the materials allows us to predict whether they float or sink? What will you need? 1. Three Legos boxes with different sizes and masses 2. One kitchen scale 3. One graduated ruler 4. One tank with water. What do we want to discover from this experience? Size Colour Mass Have wheels To determine if a body will float or sink we need to know: Only its mass Only its volume Its mass and volume Its colour Why do you think that? determine 2. Now let s make the experience Floating better Liking better Smelling better Seeing better How Do We Do It? 1. Place the water tank carefully on the table. 2. Using the graduated ruler, measure the edges for each selected box and calculate its volume. Record on a table the obtained values. 3. Using the kitchen scale, weight each of the boxes and register the values. 4. Calculate different mathematical relations between the mass and the volume for each box and for each water volumes. 5. Place, one by one, all boxes in the water and register which floats and which not. What do we observe? 1 The mass and the volume of a material can define a property when we? Divide the volume by the mass. Divide the mass by the volume. Multiply the mass by the volume Add the mass to the volume 2 When weighted all water volumes: weighted the same; the bigger the volume the bigger the mass; the bigger the volume the smaller the mass. 3 For the water, the ratio between the mass and the volume was: always the same; changing with water volume; changing with water mass. 4 When we compare the densities of the boxes with its floatability we conclude that: the ones with density higher than the water sink; the ones with density lower than the water sink; if they float or not does not depend on the density. 3. After the experience What have you learned from this experience? (you can tick more than one answer) Objects more dense than water will sink Objects less dense than water will sink We call density to the ratio between the mass and the volume of a body The density is a body property. Go back to the page 27, and check if your answer was correct. Yes, it was No, it wasn t
Experience 4: Quiz Will They Float? Teacher s Notes Topic: Buoyancy and Density Concept: For an object to float its density have to be lower than the one of the liquid. Problem: Can we predict if a body will float or sink before putting it in the water? Introduction You have probably already observed the behaviour of various objects when placed in water, some float while others sink. If we try to land a stone in the water of a lake, no matter how careful we are, it will immediately sink. But if we do the same with a piece of wood, no matter how high we let him fall, it insists on keeping close to the surface, floating. If we reduce the size of the stone it will continue to sink while the wood will continue to fluctuate even if it has the size of a tree. What properties determine whether an object floats or sinks? Materials One object collected by the students. A large tank with water. A kitchen scale A graduated ruler A large beaker of 1000 ml. A 500 ml graduated cylinder. A rubber balloon. Experience Implementation Each group will star by choosing one object for the experiment. 1. Using the kitchen scale, weight the object and register the obtained value. 2. Next they submerge completely the body in a beaker full to the top of water. The beaker should be placed previously inside the tank to collect the spilling water. If the body floats, one should be careful when submerging the body to not touch the water with their hands. Register also at this point if the body floats or not. 3. Collect the spilling water measuring its volume with the graduated cylinder. 4. Compute the ratio between the obtained mass and volume for the object. 5. Verify if the determined density is in agreement with the observation concerning the floatability of the object. Experience Guidance At the beginning teacher should ask: What do we need to measure to predict if a body will float or sink when placed on water? Submerging the body for measuring its volume will only be efficient with objects which do not absorb water and if made in a way that only the volume of the object is responsible for spilling the water from the full beaker. So, particular attention must be placed on volume determination especially if the body floats. The teacher must instruct students about these facts and tell them how to proceed. After the measurements take place, teacher must ask: What value for the density one must obtain for an object to float? At the end he can question students about two things: What they think it would happen if the density of the body was equal to the one of the water. In this stage he can fill a rubber balloon with water, carefully take out all air and close it with a knot, put it in the water and discuss with the class what they observe. Why the icebergs float if they are made of the same water of the ocean? Can they plan an experiment to discover why? Throughout This Experience The Students Should Be Able To Realize That: The determination of the density of a body allows us to preview if it floats or sinks when placed on water. A body with density equal to the water will not floats or sinks; it will remain stationary inside the water.
Student Sheet 1. Preparing the experience Can we predict if a body will float or sink when placed in water? What will you need? 1. One object collected by the students. 2. A large tank with water. 3. A kitchen scale 4. A graduated ruler 5. A large beaker of 1000 ml. 6. A 500 ml graduated cylinder. 7. A rubber balloon. 2. Now let s make the experience How Do We Do It? 1. Place the water tank carefully on the table with the beaker full of water inside at its center. 2. Using the kitchen scale, weight the selected object and register the value. 3. Carefully submerge the object without touching the water. 4. Determine the object s volume by measuring with the graduate cylinder the spilled water. Register the value and indicate if the body floats or sinks. 5. Compute the object density dividing the obtained mass by the measured volume. Size Colour Density Have wheels affect Earing Sinking Smelling Seeing What do we observe? When placed in water the object? Sink. Floated. 2 Comparing the density of the object with the water we see that: The object is denser than water and it sinks. The object is less dense than water and it floats. The object is denser than water and it floats. When placed on water which objects floats better? The red objects The objects less dense than water The objects with density equal to the water 3 When the body with density equal to the water was placed in water it: Sink. Floated Neither sink nor float, just stayed in the middle of the water. Why do you think that?
3. After the experience What have you learned from this experience? (you can tick more than one answer) We can measure o body s volume trough the water spilled from a full glass We cannot predict which bodies will float and which will sink Knowing the density of a body we can anticipate its floatability Bodies with density equal to the water don t sinks or floats, just stay inside the liquid. Go back to the page 34, and check if your answer was correct. Yes, it was No, it wasn t Finally think - if icebergs are made of the same water of the oceans why do they float? The mass of the frozen water is lower than the liquid water resulting in a lower density The volume of the frozen water is bigger than the liquid water resulting in lower density The icebergs are not made of water Plan an experiment to verify if your answer is correct.