Sink or Float?

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Students will be able to predict an items ability to float or sink and give a reason.

Big Idea

Weighing pumpkins and placing them in water helps students understand the relationship between volume and mass.


10 minutes

Gather students on the rug using a preferred classroom management technique. I like to use my “Stop, look, listen.” The students stop what they are doing, look at me and listen for the direction. I usually preface the direction with, “When I say go…” This reminds the students to listen to the whole direction before moving to follow the directive.

In this case I would say, “When I say go I would like you to clear your space, push in your chair and go take a spot on your dot. Walking feet go.”

By saying “walking feet” I am reminding the students to use walking feet in the classroom to ensure safe movement between areas.

When all of the students are seated on their dot in the rug area I hold up a small pumpkin and ask the students, “Do you think this pumpkin will sink or float?”

I select a student who is following the correct classroom protocol of raising their hand to respond to the question.

“Colin thinks the pumpkin will sink. Why is that Colin?”

“Colin thinks the pumpkin will sink because it is round, hard and heavy like a rock. I like all those adjectives words you used to describe the pumpkins attributes.”

“Raise your hand if you agree with Colin that the pumpkin will sink.”

“Okay. Raise your hand if you disagree with Colin.”

I select a student who has raised their hand and ask, “Why do you disagree with Colin?”

“Addisyn says the pumpkin will float because she has seen this before in her Pre-K class. Did you test lots of pumpkins or just one pumpkin?”

“Addisyn’s class just tested one pumpkin and it floated. So would it be fair to say that all kinds of pumpkins float?”

I select a student who has raised their hand to respond.

“Your right Leslie; scientists test many subjects before they draw a conclusion.”

“Today at one of your work stations we are going to weigh and test many types of pumpkins before we decide if pumpkins truly sink or float. Then we will discuss why.”


I use this discussion to engage my students’ attention, elicit prior knowledge and provide the students with some appropriate vocabulary. 


45 minutes

I have the students take a seat around the edge of the rug by singing the “Edge of the Rug” song.

“When you are at this work station each of you will be assigned a pumpkin to weigh and measure the circumference. The circumference is how round it is.”

“When you weigh the pumpkin you will need to zero out the scale by pressing the button here (I press the button on the scale). When you see the two zero’s you will place the pumpkin on the scale and let it go. When the scale beeps the number that appears in the little window is the number you write down on your recording sheet.”

“Next you will measure the circumference of the pumpkin. You will take a string and pinch one end. Hold that end tightly on one side of your pumpkin. With your other hand drag the string around your pumpkin until thumb meets thumb. Now here comes the tricky part, keeping both pinchers in place, take your string and put one pincher on the end of the tape measure and stretch the string out until the string is straight against the tape measure (I have the measuring tape taped to the floor so it does not move) and read the number you see by your second set of pinching fingers. Record that number.”

“When you have both numbers come and tell me and I will write it up on group chart on the SMARTBoard.”

“Once everyone has completed their measurements we will go ahead and work as a group to predict if the pumpkin will sink or float.”

“When we have the predictions filled out we will go ahead and test our predictions.”  

“Does anyone have any questions?”


I send the students over to the integrated work stations one table group at a time to maintain a safe and orderly classroom. It usually sounds like this;

“Table number one go get ready to have some pumpkin fun.

Table number two, you know what to do.

Table number three, hope you were listening to me, and

Table number four, you shouldn’t be here anymore.”


Allow the students 18 minutes to work on the activities. After 18 minutes are up, the timer goes off and the students clean up and get ready to switch stations.  

I set the visual timer and remind the students to look at it so they can use their time wisely.


At the pumpkin sink and float station the students will find all the equipment they need to get the required information. There is:

  • An electronic scale
  • A tape measure taped to the floor
  • A variety of pumpkins
  • A set of pencils 
  • A large tub of water.

As the students collect the required information I record it onto the group chart I have loaded onto the board.

Our pumpkin selection

Measuring our pumpkins.

As a group we predict if each student’s pumpkin will sink or float and fill in our choice on the chart. An individual is allowed to go against the group consensus. They must give a reason, but they can make a different choice.

Our prediction and result chart.

Discussing our predictions.

Next each student places the pumpkin they weighed and measured in the tub of water. We fill out the results on the recording chart.

Testing to see if pumpkins float.

Performing our test.

Now I pull out a small pumpkin I have cut the top off and hollowed out, a plastic boat and a rock. I place all three items into the tub of water and ask the students to discuss what they observe.

When the students have commented on what they observe I explain, “Kyle noticed that the pumpkin was hollowed out like the boat and had curved sides like the boat. The boat and the pumpkin both hold air which decreases their density and makes them lighter than the volume of water. The rock holds no air so the rock is dense and heavy which makes it sink.”

If time allows we may test a few other items using the students’ knowledge to predict whether the item will sink or float.     


In this activity the students are exploring how size and weight does not matter, but density does matter.  


At another work station the students use a paper plate and other materials to create the parts of a pumpkin which helps them to see how large a pumpkin's cavity is – thus supporting its ability to hold air.

Students working on creating their model pumpkins.

Student sample of model pumpkin.


At another work station the students use the laptops to watch Sink or Float with Annie and Moby on BrainPopJr. If they get done before it is time to switch stations they can do the game, work on the quiz or do the drawing activity.  


At another work station the students are given a piece of aluminum foil and told to create a boat. The students are told that later in the day their boats ability to float will be tested by placing pennies in it until it sinks. We will record how many pennies the boat holds in their science journal along with a photo of the students and their boat (engineering).

Students working on creating their foil boats.

Student samples of foil boats.

Testing our foil boats.


These activities provide the students with the opportunity to apply and expand their understanding of the concepts within new contexts and situations thus elaborating on the information they have been presented with. 


10 minutes

When the time is up I blow two short blasts on my whistle and use the “Stop, look, listen” technique mentioned above.

“When I say go, I would like you to clean up your space remembering to take care of our things, push in your chair and take a spot on your dot. Walking feet, go.”


“Team 203 your exit ticket today is to tell me one thing that floats and why. Remember you will need to use a complete sentence when giving your answer. For example, “One thing that floats is …””

“When you have told me your information you may use the hand sanitizer and get your snack.”

I use the fair sticks to determine the order of the students.

If a student is unable to give me an answer, they know they can do one of two things.

  1. They can ask a friend to help, or
  2. They can wait until everyone else has gone and then we will work on coming up with something that floats together.


I use this exit ticket process as a way for the students to explain what they observed from the lesson we just did. This quick assessment process allows me to see if the student is able to take information learned in one format and be able to transfer it to another format.   


In order to assess if my students have successfully understood and retained the information presented in the lesson I evaluate each student by providing them with a task the next day for morning work. For this assessment I have the students write in their science journal responding to the morning work prompt, “Draw and label four things that float.”

Some students will attempt to write the answer themselves and others can have an adult act as a scribe.

For this assignment I want the students to think carefully about what we learned yesterday and be able to explain to me why they selected the items they drew in their science journal.