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Sink/Float Discovery Bottle

Grades: K-4
Author: Diane Zak
Source: Adapted from Mother Goose Asks "Why?", Discovery Bottles


This lesson uses a "Sink/Float Discovery Bottle" to teach students how to conduct a simple investigation, use simple equipment to make observations, use observations to arrive at a reasonable explanation, and to communicate their findings and explanations. This lesson will also teach students about the properties of objects that sink and float.


What should students know as a result of this lesson?

  • Students should be able to explain which types of objects will sink and which types of objects will float.

What should the students be able to do as a result of this lesson?

  • Predict an object's ability to sink or float by observing its physical attributes.
  • Classify and sort items into groups of sinkers and floaters.
  • Communicate data by using a data collection sheet.
  • Develop their own definition about what sinkers and floaters have in common.


  • 1 1-liter bottle about 1/2 full of water per student. The teacher may want to put "catch pans" or trays under students' bottles in case of splashes or spills.
  • A collection of small objects: heavy, light, made of a variety of materials such as plastic, wood and Styrofoam, objects with holes and objects that have different shapes.
  • Towels for clean-up



Review PREDICTING with the class: The idea (hypothesis) from previous experience is used to make a prediction (what you think will happen) that can be tested.

EXAMPLE: Two balls (one large: volley ball, one small: golf ball) or (one heavy: soft ball, one light: tennis ball)...Which ball will hit the floor first when both are dropped from the same height and dropped at the same time?

Test your predictions:

  • Drop both balls at the same time from the same height; observe (Both balls will hit the floor at the same time.)

*It may be necessary to drop the balls a few times to make sure they are hitting the floor at the same time. Tell the students that when they made a guess about what would happen to the balls, they were making a prediction. Scientists make predictions about what they think will happen when they test something. Tell the students that today they will be making predictions - they should use what they already know to make their predictions.

  • Ask the students to tell their experiences with sinking/floating. What does it mean when an object sinks? What does it mean when an object floats? When you go swimming, what kinds of toys float? What can you wear to help you float? (rings, arm wings, life preserver) Are there toys that you want to sink? (Objects to dive for and retrieve) What do you think makes them sink? Why do you think boats float?
  • Each student will be given a bottle with several objects in it. Look at the objects and decide which ones you think will sink and which ones you think will float.

Assessment: Use the students' input to make a class chart or poster illustrating the steps involved in making predictions.

  1. make careful observations, using their five senses
  2. past experiences and prior knowledge
  3. guess what will happen next

*If the students need help with the answers, prompt them - What was the first thing they did with the balls? (Looked at them, touched them, lifted them). What was the second thing they did before the balls were dropped? (Made a prediction/guess about which ball would hit the floor first). What was the last thing they did? (Dropped the balls to find out if their predictions/guesses were correct).


Allow the students time to observe and make predictions about which objects, in the bottle, will sink and which objects will float.

  • Record their predictions on their data sheet: Name of object to be tested, Prediction: What will happen?
  • Depending on the age of the students, they should either fill in the data sheet or draw pictures of their predictions. Example: on 1/4 of the paper draw pictures of objects they predict will float and on 1/4 of the paper draw pictures of objects they predict will sink.
  • Students should test their predictions by filling the bottle with water.
  • Record their observations on their data sheet. On the other half of the data sheet write or draw pictures of the objects that floated, the objects that sank, and finally the objects that surprised them.
  • Talk with the class about your predictions. Which ones were correct? Which predictions were not correct?

Assessment: Monitor the students' work to make sure they are following the correct procedures, making observations, and recording data accurately. Redirect their attention to the task, as needed. Make sure students are employing safe practices as they conduct the experiment. Answer students' questions regarding procedures.


Students report their findings.

  1. Based on your findings, what general statements can you make about the objects tested?
  2. What do the sinkers have in common?
  3. What do the floaters have in common?
  4. Are there some objects that both sink and float? Create a category for those objects as well.
  5. What do the sinkers/floaters have in common?
  6. What conclusions can you make about the objects tested?
  7. Can people float? Explain your answer.
  8. In your own words, what definition would you give for objects that float?
  9. In your own words, what definition would you give for objects that sink?
  10. In your own words, what definition would you give for objects that both sink and float?

Assessment: Listen to students' accounts of their findings to judge if their reports are supported by the findings that you observed as experiments were being conducted. Ascertain knowledge of sinking and floating by asking questions. See above # 1-10. Make a class poster illustrating and labeling what you learned about objects that sink and objects that float. Older students could make a cartoon, with a minimum of 5 or 6 sections, explaining the kinds of things that sink and the kinds of things that float. Younger students could draw a picture depicting things that sink and things that float.


  1. Look at the objects that sank. Describe them. Do they have anything in common with each other?
  2. Look at the objects that floated. Describe them. Do they have anything in common with each other?
  3. Compare their results with the rest of the class. Did everyone get the same results? If not, replicate their trial.

* If they find it necessary to replicate their trial, this would be a good time to talk to the class about how important it is for scientists to do an experiment many times to make sure their results are accurate. If an experiment does not turn out as expected, it does not necessarily mean you did anything wrong. A failure raises more questions, which leads to more inquiry and more tests.


  1. Who Sank the Boat? by Pamela Allen (1996) Putnam Publishing (book about a cow, donkey, sheep, pig, and mouse who decide to go for a boat ride)
  2. I Love Boats by Flora Mc Donnell (1995) Candlewick Press Massachusetts
  3. Step Into Reading Boats! by Shana Corey (2001) Random House New York

Assessment: Ask questions to ascertain students' understanding of things that sink and things that float. See above # 1-2. Cut out pictures from magazines. Create a poster with pictures of objects that they predict will sink on 1/2 of the poster board and objects that they predict will float on the other 1/2 of the poster board, based on their conclusions from their prior experiments.


No prerequisite skills are needed.

Best Teaching Practices

  • Hands-on Teaching
  • Questioning
  • Inquiry

Alignment with Standards

NGSS Standards:

  • 2-PS1-1 Plan and conduct an investigation to describe and classify different kinds of materials by their observable properties.
  • 2-PS1-2 Analyze data obtained from testing different materials to determine which materials have the properties that are best suited for an intended purpose.

National Standards:

  • Content Standard A: K-4 Science as Inquiry
  • Content Standard B: K-4 Physical Science

Ohio Standards:

  • Grades 3-5 Scientific Inquiry
  • Grades 3-5 Physical Science

Content Knowledge

Predicting: What do you think will happen? The idea (hypothesis) from previous experience is used to make a prediction that can be tested. A hypothesis is an educated guess, based on observations and experiences. Correct or incorrect predictions, in science, don't matter. What does matter is that the prediction leads us to a test that can lead us to the truth. We make predictions when we guess the outcome of an experiment.

Making careful observations provides us with information. We can use this information to make predictions about possible answers to our questions. Our answers are based on our observations and previous experiences. We make predictions in every day life. Example: Will it rain? Based on our observations of wind direction, clouds, and humidity, we can predict whether it will rain. We can predict which amusement park ride is the most thrilling. A prediction must be one that can be tested. One possible way to test this might be to take your pulse before getting on any ride. At the end of a ride, immediately take your pulse. The ride that causes your pulse to increase the most might be the most thrilling.

If the density of an object is less than the density of water, it will float. If the density of an object is greater than the density of water, it will sink. The density of a fresh egg is greater than that of an older egg because it loses water through the tiny pores in the shell. So, don't eat an egg that floats in fresh water. It's spoiled. If you save an egg several days past the expiration date, you will be able to demonstrate this to the students. Keep checking the egg at home to make sure it is ready to float in time for your demonstration.

Demonstrate how the density of water may change: Place a fresh egg in a clear glass of water. It should sink to the bottom. Gradually add salt. As more salt is added, the egg will begin to float. You can get the egg to remain in the center of the glass before it floats to the top. (Sink and float at the same time - neutral buoyancy). By continuing to add salt, the density of the water is increasing. The egg will eventually float on top of the water.


Remind students to use materials for the intended purpose; no horseplay in the lab; do not to put objects in their mouths; do not share materials with the other students. Be careful about spills; report any spills to the teacher.


Knowing what sinks and what floats is necessary when building boats, ships, and submarines. It is useful for making flotation devices for swimming such as "wings" for arms of young children, rings and chairs that float, life jackets, life preservers and using the technology that allows some airplanes to land on water.


See Learning Cycle, Exploration, and Elaboration Assessment, Student worksheet

Other Considerations

Grouping Suggestions: Grouping is not necessary

Pacing/Suggested Time: Two class periods

Printable PDF Worksheets

Data Sheet