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WHAT FLOATS YOUR BOAT?
Grades 6 - 8

Overview

Children and adults alike may find difficulty in explaining why some objects float while others sink. For example, why does a boat weighing several tons float, while a pebble weighing a fraction of an ounce sinks? This lesson is designed to introduce your students to the concept of buoyancy. The Video used in this lesson demonstrates and explains the characteristics of objects that sink and float. It presents the concepts of displacement, weight, and buoyancy. This lesson will also lead to future lessons on the concept of density.
ITV Series
"Bill Nye the Science Guy: Buoyancy"
Learning Objectives
Students will be able to:
Materials
Teacher:

Student:
(Per group of 2 students) -
Vocabulary
Displacement: the amount of water moved out of the way by an object placed in it.

Weight and Mass: Mass and weight are used interchangeably for the purposes of this lesson.

Buoyancy: the ability to float.
Pre-Viewing Activities
In order to get the students thinking about sinking and floating perform a simple demonstration using an assortment of solid (not hollow) object made from a variety of materials. Ask a student to come to the board to record the results.

"Today we are going to learn why some things float, while other things sink. I have in front of me many objects. One by one, as I drop them into the water, I will ask you to predict which will sink and which will float." Your students will probably be able to make most predictions correctly. Try to use a few materials like ceramic, rubber, aluminum foil, or plastic which they may not be as sure about. After testing each object, and recording the results on the board. Ask them some questions that you do not want them to answer out loud yet. "Why did x, y, and z materials float? What characteristics do they have?" Why do x, y, and z materials sink? What characteristics do they have?" "How can a boat float when it is made from some of the same materials you saw sink?" These are the kinds of questions that we will be able to answer when we are done today."
Focus Viewing
"Now we are going to view a video that will help us answer these questions."
To give students a specific responsibility while viewing, say...
"As you watch this video, list all terms that describe why things float. You do not need to define or explain these terms at this time; just list them."

Viewing Activities
BEGIN tape immediately following the lead-in when the narrator says "Bill Nye the Science Guy: brought to you by boats...."

PAUSE tape immediately when the word "displace" appears at the bottom of the screen to check if students have identified the two terms that describe why things float that have already been mentioned in the video. At this point you only need to make sure the students have listed "buoyancy", "weight of water" and "displacement". They need not define or have notes on the terms yet.

RESUME tape.

PAUSE tape when Bill Nye is sitting on top of the dunk tank,and says "....I am going to displace some water". Ask students to predict what will happen to the water level. After receiving an answer of "the water level will rise", ask the students how much it will rise.

RESUME tape.

BEGIN tape immediately following the lead-in when the narrator says "Bill Nye the Science Guy: brought to you by boats...."

PAUSE tape immediately when the word "displace" appears at the bottom of the screen to check if students have identified the two terms that describe why things float that have already been mentioned in the video. At this point you only need to make sure the students have listed "buoyancy", "weight of water" and "displacement". They need not define or have notes on the terms yet.

RESUME tape.

PAUSE tape when Bill Nye is sitting on top of the dunk tank,and says "....I am going to displace some water". Ask students to predict what will happen to the water level. After receiving an answer of "the water level will rise", ask the students how much it will rise.

RESUME tape.

STOP tape after Bill fills the mold of the bottom of the boat and say, "Isn't that cool", to fill-in notes on the terms which they have collected so far. First say to the students..."define buoyancy in your own words." Instruct the students to share their definitions. Keep taking answers and directing the discussion until a definition is developed that defines buoyancy as: the ability to float. Instruct the students to write down this definition.

Next say to the students,"define in your own words the word displacement." Ask students to share their definitions. Keep taking answers until a definition is developed that defines displacement as the amount of water (fluid) pushed out of the way by an object placed in that water (fluid).

Now say to the students..."I would now like you to come up with statement that relates the term weight of water to displacement and buoyancy." This statement will probably be a couple of sentences. Be sure when students share their answers that they include: The weight of the water causes objects to be buoyant, The weight of the water displaced by the floating object is equal to the weight of the object.

Press PLAY and REWIND tape to the beginning of the segment where Bill is in the lab and is going to demonstrate with the boat.

PAUSE and ask for volunteers to narrate the tape as it is replayed with the audio muted. (You usually have at least one performer in every class). Tell them they can use their notes as the segment is playing.

PLAY tape with the audio segment muted. This will help to reinforce concepts and check for comprehension. Feel free to do this multiple times if you have several volunteers.

After the final volunteer has gone, PAUSE and FAST FORWARD to the segment where Bill is back in the lab with an aquarium and a model of the Titanic and PAUSE the tape.


Focus For Viewing:
To give the students a specific responsibility while viewing, segue into this segment by saying..."Now we know why things float. After watching the next segment I want you to be able to explain why things sink."

RESUME tape.

PAUSE tape at the end of this segment to check for comprehension. Ask the student to share their ideas on why something sinks. It went by kind of fast, so you may want to REWIND and PLAY the segment again if the students aren't coming up with the answer: Things that displace less water than they weigh will sink. When you are satisfied that the students have a basic understanding you may STOP tape and you are done with the video portion of the lesson.
Post-Viewing Activities
"We now have been presented with the basic information about floating and sinking. Next we are going to test for ourselves whether or not the information is correct."
1) Have the students work with a partner.
2) Provide each group with a one 100mL graduated cylinder, one small beaker or cup, objects like the ones that you used in the pre-viewing demonstration, and a balance.
3) Instruct the students to fill their graduated cylinders to the 50mL mark.
4) Gently place the objects one-by-one into the graduated cylinder.
5) Record the level to which the water rises in a data table.
6) Subtract 50mL from each resulting level to find the displacement caused by each object.
7) Weigh (mass) each object on the balance and record their results.
8) Weigh the beaker.
9) Measure out in a graduated cylinder the amount of water displaced by object #1. Pour the water into the beaker and find its weight. Record the result in the data table, and repeat for each object.
10) Find the weight of the water displaced by subtracting the weight of the beaker from each of the weights found in step 9.
11) Students answer orally the following questions: Is the weight of the water that was displaced nearly equal to the weight of the objects that float? Is the weight of water that was displaced more or less than the weight of the objects that sank?
12) Conclude by reinforcing that the weight of water is what keeps things afloat.
13) Assessment: Provide the students with Aluminum foil or molding clay that would by themselves sink. Instruct the students to design and construct a craft that will float.
Action Plan
Contact boat building companies by letter or phone and ask them to send information on boat specs and other related information on their boat designs and buoyancy.

Develop a contest for other students at your school to build boats. The challenge is to use specified materials to design and build a boat that can hold the most weight.
Extensions

Music:
Write a silly song or rap that explains buoyancy.

Art:
Design and produce a trifold pamphlet on buoyancy complete with text and illustrations.

Language Arts:
Write a poem that explains the various aspects of buoyancy.

Science:
Continue with the theme of buoyancy relating it to density. Design experiments that change the "weight of water". See if you can get objects that float in water to sink in other liquids of different densities and vice versa.

Social Studies:
Search the library for examples of historically significant events that deal with buoyancy.

P.E. or Extracurricular:
Form a Scuba club. Find a group of students that is interested in learning scuba. Be sure to have them report back to class their experiences, and the importance of understanding buoyancy in this sport.

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