MnSTEP Teaching Activity Collection > MnSTEP Activities > Sinking and Floating Water

Sinking and Floating Water

Nancy Thill, Pilgrim Lane Elementary School, Plymouth,MN, based on an original activity frm the FOSS Kit, Water, Investigation 2 p. 14
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Students will become familiar with the concept of density in relationship to objects sinking and floating. Once an understanding is built that objects that are less dense than water will float and things that are denser will sink, they will make predictions and observe what happens when colored hot water is placed into room temperature water. A similar procedure will be done by placing colored cold water into room temperature water. They should observe that the less dense warm water will rise and the denser cold water will sink.

Learning Goals

Students will learn that objects that are less dense than water will float, and objects that are denser than water will sink. Students will discover that warm water is less dense than room temperature water and cold water is denser than room temperature water. By deductive reasoning skills they may communicate that cold water is denser than warm water. They will need to use their skill of using a thermometer to measure the temperature of the water. Students will use observation skills as well as collect and record data. They will need to use cooperative group skills in which each child has a specific job to complete the activity. Vocabulary that is reviewed for this lesson includes the following words: density, sink, float, and inquire.

Context for Use

This activity is best for students between grades 3-5. This activity would be done as a lab in the classroom and will take approximately 30-40 minutes. There could be follow up activities once this activity is complete that will be noted later. It is important to have established good cooperative learning routines and jobs in place prior to performing this (or any other) lab activity. Students should already be familiar with reading a thermometer and recording information on data sheets. Groups of 3-4 students who are grouped heterogeneously work best. Class size may vary. (I will be making 8-9 groups with 3 or 4 students in each group.) This activity could be performed by an individual, but they would miss out on the cooperative learning that should take place as well. A material station in the classroom should be established and maintained for the school year so that children know where to collect and return materials necessary for any labs. For this activity each group will need the following: 2 large clear plastic cups, 2 rubber bands, 2 craft sticks, 2 small plastic vials, 2 clothespins, and student data sheets (one for each child in the group) and one thermometer. For the whole class these items are needed: 2 pitchers of room temperature water, 2 dispensing bottles prepared ahead of time - one has red colored hot water, the other contains blue colored cold water. (Use food coloring to add the color.) Keep these dispensers in a thermos or cooler to maintain the temperature. A wooden bead, a cork, a penny and a stone will be used in a teacher demonstration prior to the lab the students will do. This activity is done after students have done some initial work with properties of water. Since the water cycle is a 4th grade standard this lesson could be tied in when doing other water studies such as pond life, or if studying phenology - when lakes are turning over.

Subject: Chemistry:General Chemistry:Properties of Matter,
Resource Type: Activities:Classroom Activity
Grade Level: Intermediate (3-5)

Description and Teaching Materials

This activity is part of a Foss unit on water-Investigation 2 Part 2 with slight variations. Begin with a whole class discussion on what the students predict will happen when various objects are placed in a bucket filled with water. Ask students what helped them in their background knowledge to make this prediction. As a demonstration put each item one at time (cork, stone, wooden bead and penny) in the water after each prediction. Ask students what makes things sink or float. Introduce the concept that items that are less dense will float, and those that are denser will sink. Now ask the question of what would happen if hot water is placed into room temperature water. Show students how to assemble the vials with rubber bands around the craft sticks and how once the hot water is put into the vial how to carefully place them into the clear plastic cups with the clothespin. Once the whole group discussion is complete, send the students back to their science groups. (These would be established prior to this activity. Groups of 3-4 students can be formed where one child is the materials manager and gets and returns equipment. A second teammate is the starter and tracker. This is the person who assembles or does the first step of the process and then allows each member to perform a part of the set up. This person watches the time as well as makes certain that everyone in the group participates. This child may ask, "What did you notice?" or a similar question to each group member. A third group member will be the data collector. He or she will record the observations on a sheet. Once the experiment is complete, the data collector is responsible for making sure the other group members get that information in their own personal journals. A fourth job is that of reader and reporter. That child is the one who reads the information on the data sheet and communicates for their group when we discuss as a whole class what was observed. All group members will be respectful and encourage each other.) Have the materials people come to get supplies. The starter will assemble the "dippers" and fill the larger cups with room temperature water. All group members should practice dunking the dippers into the cups of water. Have one of the group members measure the temperature of the room temperature water. Have the recorders verify the temperature of the hot water that the teacher will use. For safety purposes, the teacher can come around and fill one of the two dippers with the hot water. All students should observe what happens. Have students stop with the equipment so you can discuss their observations. Remind them that the reporter is the one who tells the results for their group. Predict what might happen if we try the same thing with cold water. Perform the same procedure. Have the recorder/reporter verify the temperature of the teacher's cold water before it is put into the vials. Discuss the observations when cold water was used with the whole class. Materials people return supplies to clean up. Have groups record 3 big ideas that came to mind or things that were learned from this activity. Resources: Foss Science kit on water. Investigation 2 p. 14, student sheet #7 Sinking and Floating Water, Foss Science Story "The Pond" p.6

Teaching Notes and Tips

Many students will confuse the terms of more dense and less dense. Give many samples to expose them to the notion that density does not mean weight. Show the same sized pound cake vs. angel food cake, the old joke about "which weighs more... a pound of bricks or a pound of feathers?" A lesson that comes later in this Foss unit deals with the porosity and permeability of types of soils, so an initial understanding of density may help with some connections to those terms in a general sense. Using the hot water may pose some safety concerns, so it works well for the teacher to put the hot (and later the cold) water in the vials. One tip is to remind the students not to say their observations aloud because you may not have gotten to the other groups before the hot water rises. We want the students to notice this for themselves. Carefully going over jobs and who does each part will help alleviate any arguments. Reinforce that each job is important and valued. The part of this activity that I would make different from how Foss presents it would be to add the component of measuring the temperature of the water samples being used, and the evaluation at the end. I think that children have experiences with swimming and living near lakes that could help them with some deductive reasoning. Extension Activities: Have students role play being water molecules. Hot molecules would be spread out, cold ones "shiver" and stay close together. Visit a nature center or nearby pond for a pond study after reading children's books about ponds and the science story called, "The Pond" that is part of the Foss kit. Take notice of the times of the year when lakes are turning over. Discuss convection and how other liquids and gases are a part of this with tectonic plates and weather.


For this activity I would use an informal assessment and listen to group discussion as I go around with the liquids. I would check each group's "3 big ideas" paper that they wrote when finishing the activity. I would have them add on the back of their data sheet a picture of how they could show the hot, cold and room temperature water all in one cup with a brief explanation of why they colored the picture the way they did.


Science: 1.B.2 2.A.3 Math 4.A.1

References and Resources

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