Sinking and Floating Along

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SWBAT determine the properties of objects that sink or float by placing a variety of objects in a tub of water.

Big Idea

Children often misunderstand what causes an item to sink or float. This lesson lets them experience placing a variety of objects in water and identify what characteristics the objects have in common.


10 minutes

I call the kids one table team at a time to sit on the floor and look like scientists. When they hear, "Sit like scientists," they know that I am expecting them to sit crisscross apple sauce with their hands in their laps. They are expected to have their mouths closed, their eyes and ears on the teacher, and their brain ready to learn. I do this to get them ready to think and toe hold them accountable for their behavior. 

I engage the kids with a quick personal reflection story, a question and discussion:

I tell the kids about how I was cleaning my pool one day and I noticed that some things were floating in it and others were sitting at the bottom in the deep end. It made me wonder what makes some objects sink and some float. I pose the question to them, "What makes things sink or float?" 

I record the question on a piece of chart paper. This sets the tone for the lesson and gets the kids thinking about what we will be exploring today.

I then ask the kids to think silently in their brains for a whole minute to which I set the timer on my phone. I ask them to think about how they might find out how objects float. What could they do? What could they use?

Once the minute is up, I have the kids turn to their talking partner and share their ideas. I ask the kids to stand up, which helps with blood flow to the brain, and tell them that the shorter person will share first. Each person gets 30 seconds to explain what they thought. I set the timer on my phone for 30 seconds for each partners turn to share. I do this so everyone is held accountable for speaking and participating and so each person gets equal time and one doesn't dominate over the other. 


15 minutes

I model for the students how to plan an investigation.

Still seated on the floor, I show the kids the tub of materials I brought in for this lesson. In the container there is the following:

6  one quart clear containers

1  water pitcher 

I have a sink in my classroom. If you don't, plan on bringing in four 1-gallon bottles of water.

pond rocks


empty plastic easter eggs


pieces of plastic drinking straws

Hot Wheel or Matchbox cars

2x2 pieces of index cards

small styrofoam cups

small party pumpkin treat containers

a variety of other random items

*Please note that not all of the tables have to have the same items to sink and float

I ask the kids what they could do with all of this stuff to find out what sinks and what floats. I call on kids at random by pulling names from a name stick can. I record their ideas as they start to formulate into a viable experiment. My job is to guide the format of the experiment as they provide the information. I know this because past experience with my kids revealed that they grasp the concept of designing a plan to test a question, but they struggle with how to put it in order.

Within minutes we have a functional experiment designed and ready to implement. I explain that we aren't going to waste any time. We are going to get to work right away.


Once we are finished listing the plan, I call one table leader at a time to pick up one of everything they will need. 

After the table leaders are all sitting with the materials for each table, I dismiss the rest of the class one table team at a time to join their table leader. 

I tell the teams to place all of their materials in the middle of the table. I then ask them what we need to do next. They can't help but yell out, "Give us water!"

I ask them how I should do that and they ask me to fill the pitcher and pour it into each table's container. 

I don't tell them what I should do because I want them to be the scientists and make the decisions.

Once the tables have their materials I tell them that they can only put ONE object in the water at a time and watch what it does. They also have to draw a picture of each object on the recording sheets that the helper of the day is about to hand out and write an "S" for sink or an "F" for float next to each picture. I demonstrate what I mean for them. I draw a rock in one of the boxes and I tell them that if I see it sink when I put it in the water I'll write an "S" next to it. If it floats, I'll write and "F".

The kids are informed that they have 8 minutes left to complete the experiment.


I explain what I expect from the kids as they complete this experiment:

1)  keep the water in the container

2)  objects are gently placed in the container, NEVER dropped; I demonstrate using a rock

3)  Use time wisely; we only have a few minutes.

Anyone breaking the rules is removed from the table and asked to sit on the floor to watch rather than participate.


10 minutes

Once the kids are finished watching their objects sink or float, I have the table leaders collect all the materials and leave them in the center of the table. I pick them up and spill out the water while they work on their independent assignment.

I call one table at a time to the floor to sit like scientists. I instruct them to take their observation sheet to the floor with them. 

I create a graph on the chart that lists the table names and the objects. I record what the each table saw the objects do. 

When we are finished recording each tables' information, we go over it to make conclusions. Some of the items recorded are:

Float               Sink

feather            rock

straw               car

plastic egg       metal spoon

toothpicks       screwdriver



There is a controversy with the piece of index card. Some tables say it floats, some say it sinks and one says it does both. I ask that table what they mean. They share with the class that they put it in the water first and it floated, but by the time they were done observing the rest of the objects, it had sunk. This is a great way to get scientific discussions going. Having the kids use evidence from their observations get the kids acquainted with scientific argumentation and can be built upon as they progress through the grade levels.

This brings me to the next question:

Why do some objects sink and why do some float?

Now that the kids have identified the objects that sink and float, I want them to get back to the original question, WHY?


5 minutes

While still seated on the floor, I ask the kids to think about why some objects float and why some sink. What do they have in common?  I again have them think for one whole minute silently to themselves and then share with their floor partner - each getting 30 seconds to speak.

Once they are finished sharing their thoughts with their floor partners, I ask for volunteers to tell the class what they talked about. I record their ideas on chart paper as they talk.

After they have shared, I use the information they provided to explain about weight, air, and water absorption. 

I do it this way so the kids can create their own baseline of thinking before I go into the actual explanations. If the kids can derive their own basic understanding that weight, buoyancy, and absorption, it is easier for them to transition to understanding how these things effect whether an object sinks or floats.


10 minutes

The evaluation for this lesson is independent. It is a cut and paste sort of objects that sink and things that float.

I have the kids cut out the pieces and sort them into two columns to reflect the work they did on their recording sheets. This makes the evaluation authentic and fully representative of the activity. They then glue the completed page into their science journals. As they are working, I collect and return the materials to the tub. I have a sink in my room so I can easily dispose of the water in the containers. If you don't have a sink in your classroom, have a child hold the door open for you so you can quickly dispose of the water as the kids work.

Once I am finished putting the materials away, I walk around the room to assist students and ask them to explain their sorting to me as I check their work. This allows me to do quick individual assessments of learning. Kids who struggle with answering any questions I ask are given a quick review of the learning by asking them more questions relating to what they experienced during the exploration.

Questions that can be asked:

  • Why did you place the _______ in the sink/float column?
  • Why do you think the _______ floated/sank?


 Questions for kids struggling with making connections:

  • If the toy car sank, then what do you think will happen with a hammer?
  • What type of things floated in the water? So, which of these (pointing to pictures on work page) do you think with float?

Once all the kids are finished with their cut and paste job, I have them gather back on the floor with their science journals. They are asked to share their work with their floor partners. During this time they compare where they placed each object and discuss any discrepancies they observe.

I then call on three kids by pulling three name sticks from a name stick can and having each come up one at a time to share their learning and answer questions the other students may have. I limit the questioning to a max of three questions per presenter to save time. I thought the kids would be anxious about answering peer questions, but it turns out that they look forward to showing off what they know, even my shy kids!