Underwater Volcano Authors: Christian Bertsch, University of Vienna years

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1 9-11 years Science Content: Physics Target Concepts/Skills: Density of solids and fluids Target Age group: 9-11 years Duration of activity: 3 hours Summary: Students inquire the concept of floating and sinking and do this by loading the same volume with different material and test if they sink or float. The link between volume and mass to form density in liquids is also explored. The inquiry leads to understanding of the concept of density through comparing different solids and fluids. The behaviour of liquids at different temperatures is also tested leading to an understanding that a higher temperature of a fluid lowers its density. Resources: Experiment 1: 3 plastic vessels (same size e.g. kinder eggs) with a cap (completely filled with sand, flour, feathers), 1 bowl filled with water Experiment 2: 1 glass, cooking oil, syrup, water, 1 grape, 1 bolt, 1 spoon, 1 cork Experiment 3: 1 beaker with cold water; small bottle; hot water; small funnel; ink Objective: By the end of the activity children should be able to: Show and explain that solids and fluids can have different densities; Indicate how density (and not size) determines if objects float or sink; and Show that the density of hot water is lower than the one of cold water. Underwater Authors: Christian Bertsch, University of Vienna 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.

2 Background information: The teacher sets up various measuring tools (ruler, caliper, equal arm scale, dynamometer, chronometer, graded cylinder, thermometer) for the purpose of triggering the students sense of curiosity and then distributes the first activity sheets. Students make predictions on the names of the measuring tools and what they believe that each of them measure. They write down their ideas on the activity sheets. The density of a material is defined as its mass per unit volume. Mathematically, density is defined as mass divided by volume. For students to understand the concept of density it helps when you use objects of the same size but different mass (for example Kinder eggs with different fillings). In general, density can be changed by changing either the pressure or the temperature. Increasing the pressure increases the density of a material. Increasing the temperature generally decreases the density, but there are exceptions to this generalization. For example, the density of water increases between its melting point at 0 C and 4 C (density anomaly of water). From 4 C to 100 C the density decreases, therefore warm water is lighter than cold water (highest density at 3,98 C = 1,00 g/cm3). One can explain this phenomenon by using the model of particles. When the temperature rises the water particles gain more energy and move more vigorously. Therefore the same amount of particles (same mass) need more space. This extension leads to a lower density as the same gas occupies a larger volume. Density of different materials at 20 C Material Density (g/cm3) Spruce wood 0,43 Oak wood 0,65 Water 0,998 Aluminium 2,67 Gold 19,30 Water particles at 80 C Water particles at 20 C

3 Experiment 1: Density Materials: 3 plastic vessels with a cap (completely filled with sand, flour, feathers), 1 bowl filled with water What property decides if objects float or sink? What do you think? Which of the three vessels will float, which will sink? Before you try, make a prediction. Material My Prediction My Observation Vessel with sand Sink Float Sink Float Vessel with flour Sink Float Sink Float Vessel with feathers Sink Float Sink Float Some vessels even if they have the same size float, others sink. Why? Do you have an idea?

4 Experiment 2: Density of fluids Material: 1 beaker, cooking oil, syrup, water, paperclip, 1 grape, 1 bolt, 1 spoon, 1 cork 1. Put 2 cm oil into the beaker. 2. Put 4 cm water into the beaker. 3. Put 2 cm syrup into the beaker. 4. Put the single objects into the three fluids. Draw your observation here below and label the drawing! Where did the single objects and fluids settle? Order the used materials and fluids according to their density. Lower density Higher density

5 Experiment 3: Underwater Materials: beaker with cold water, small bottle, hot water, small funnel, ink Have you ever been diving in a lake? Where is the water cooler? On the surface or at the bottom of the lake? Mix the ink with the hot water and put it with help of the funnel into the small bottle. Put the bottle on the bottom of the beaker with cold water. Observe what happens and draw it in the figure below. Can you explain your observation? Warm water has a density than cold water

6 What do you think will happen if you mix the ink with the cold water and put the small bottle with the cold water into the beaker with warm water? Try it out and draw your observation: