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Grades 6-8


In this lesson and its hands-on activities, the students should have the opportunity to design a simple boat and predict how much weight it can carry. The students should also discover why objects float or sink and how this can be determined experimentally. The students should gain experience in data collection, conclusion formation, and analysis skills.
ITV Series

Bill Nye The Science Guy #119: Buoyancy Mr. Wizard: How it Works: Buoyancy Science Demonstrations #13: Archimedes' Principle Dr. Dad PH3 #2: Buoyancy-Sink, Float or Boat
Learning Objectives
Students will be able to:
Per class:

Boat construction activity:
Per group of students:

Submarine construction activity:
Per group of students:

Post-Viewing Activity Per group of students:
Pre-Viewing Activities
Before beginning this activity, students should understand the concept of density.

A few minutes prior to the beginning of class, place on your desk two tall clear cylinders. Fill one with water and place a drop of blue food coloring in it. Fill the other with Mountain Dew® soda. As the students arrive, place several mothballs and two Alka Seltzer® tablets in the water cylinder. Place several peeled and unpeeled grapes in the soda cylinder.

Allow the students five minutes to make careful observations about the two cylinders and to write their detailed, descriptive observations on a piece of paper. Choose several students to share their observations with the rest of the class. Ask the students to explain why some objects moved while others didn't. Explain the preceding situation this way: the peeled grape has no attraction for the bubbles. This type of surface is called hydrophilic (or "water-loving") and attracts only the water. The bubbles could not stick to the surface. The moth balls and the regular grapes have a hydrophobia (or "water-fearing") surface. This surface repels water and gives the bubbles a surface to adhere to. When enough gas bubbles have adhered to the surface of the grapes or mothballs, they float. When the mothballs and grapes reach the surface, the bubbles burst and the objects sink. Ask the students to predict what the bubbles were made of in each cylinder. (Carbon dioxide gas should be the answer.)
Focus Viewing
The focus for viewing is a specific responsibility or task(s) students are responsible for during or after watching the video(s) to focus and engage students' viewing attention. In this activity, the focus for viewing is a guided listening sheet that the students are required to complete during the course of watching the video.

Viewing Activities
Explain to the students that today's lesson is entitled "I've Got that Sinking Feeling." Ask if anyone knows what buoyancy is (the upward push of a fluid). Ask the students to give examples of situations where they might have encountered buoyancy. (Accept all answers without giving the definition of buoyancy. If students do not respond to the question, tell them to watch the following video to learn the answer.) Distribute the guided listening sheets. Tell the students to look over their listening sheet carefully and notice how it is arranged. The first part of the sheet deals with data collection and organization. They will fill this out as they view an experiment on video. The rest of the sheet requires that they pay close attention to various videos and activities in order to obtain the correct answers.

INSERT Bill Nye The Science Guy #119: Buoyancy and start the video after the announcer says, "Bill Nye the Science Guy is brought to you by boats." PAUSE the video after Bill Nye says "Buoyancy's a great thing. It's holding us up right now." Ask a student to define buoyancy. RESUME the video. PAUSE after Bill Nye says "How much do you think the water weighs?" Ask students to suggest an answer. RESUME the video. Use a water soluble marker to mark on the TV screen and emphasize the indentation left by the boat as Bill Nye fills it up with the blue displaced water. STOP and EJECT the video after Bill Nye says "It fits exactly. Isn't that cool?" Erase the TV screen with a cloth.

INSERT and START Mr. Wizard How it works: Buoyancy. STOP the video when the girl fills in 600 grams and Mr. Wizard says "As you know, one milliliter of water weighs one gram." Ask the students if the mass of one milliliter of any liquid is equivalent to one gram. (No, this is a special relationship with pure water at 4 degrees Celsius.) Reinforce this concept by asking a student to use a balance and determine the mass of a graduated cylinder. Instruct the student to add exactly one milliliter of water to a graduated cylinder by using a plastic pipette. Ask the student to read the new mass on the balance for the class. Reinforce this concept by asking the student to tell the class the mass of one milliliter of water (one gram). Show the students the prepared cubic centimeter paper box. Ask another student to pour the milliliter of water from the graduate into the cubic centimeter box and make an observation. Ask the student to share the observation with the other students. (One milliliter of water fills up the cubic centimeter box.) Tell the students that a relationship exists with water. One cubic centimeter of water is the same as one milliliter of water and the mass of the water is equal to one gram.

RESUME the video. PAUSE after the difference data is filled in on the chart, then ask students to analyze the data and make a conclusion. Tell the students to write a conclusion about floating objects and the water they displace on their data sheets. Call on a few students to read their conclusions. RESUME the video to hear Mr. Wizard's explanation. (If something floats, then it displaces an equal volume of water as it weighs.) REWIND and play the video if the students need to hear the explanation again.

RESUME the video. PAUSE the video when the girl writes in 100 grams. Ask the students to analyze the data on sinking objects and write a new conclusion. Call on a few students to read their conclusions. RESUME the video to hear Mr. Wizard's explanation. (Even though an object sinks, it is still buoyed up by an amount of water equal to its displaced weight.) REWIND the video if students need to hear the explanation again. STOP and EJECT the video when Mr. Wizard says "Well, you've got the idea and you did a beautiful job on the chart."

At this point, let the students know that they, as teams, will be designing boats, using aluminum foil, that will float.

Prior to class, create a supply dispersal/collection chart. To prepare this chart, divide a large piece of poster board into as many sections as there are groups. Outline and number each section clearly with a marker. Cover the entire board with clear contact paper. Place the necessary supplies for each team of students in the numbered squares. Assign each team of students a number and tell them to obtain their supplies from their numbered square at the supply table. Tell them to follow the instructions on their worksheets and complete the data table. When they are finished they should replace their materials on the assigned group number on the supply chart. When the activity is completed, check to see that each group returned their materials as directed.

Ask them to predict whether objects will float in liquids other than fresh water? (Boats float in salt water.) Ask them if salt water is heavier than fresh water. (Yes, it has a higher density.) Ask if an object has to displace more or less salt water than fresh water in order to float?" (Less) Show the students two containers that contain identical volumes of liquids. Tell them one contains mercury and the other water. Pass these sealed containers around the room, allowing the students to feel the difference in weight between equal volumes of water and mercury. Ask, if they think anything can float in mercury. Accept all answers.

INSERT Science Demonstrations #13: Archimedes' Principle. START the video after Dr. Miller says "I'm going to put the ball in the vessel of mercury." PAUSE the video and ask the students to predict what will happen. RESUME the video and MUTE the volume when Dr. Miller says "What about steel?" Muting the volume at this point will focus the students' attention on the steel ball. Ask for predictions on what will happen to the steel ball.

PAUSE the video momentarily just before the steel ball is placed into the mercury. This creates a suspenseful situation with the students. RESUME the video and correct the volume. STOP and EJECT the video after Dr. Miller says "Now talking about Archimedes."

Ask if anyone ever heard of Archimedes and his principle. Tell the students that Archimedes lived in the third century B. C. and discovered that an object's volume can be calculated by the amount of water it displaces. He discovered this while he was bathing and became so excited he jumped out of his bath shouting 'Eureka! Eureka!' and ran down the street naked. His principle states that any object floating upon or submerged in a fluid is buoyed upward by a force equal to the weight of the displaced fluid. Ask students to define a fluid. (Anything that flows) Tell them this means that gases as well as liquids are fluids because they flow. Hot air balloons rise when they displace their weight in air and boats float when they displace their weight in water.

INSERT Bill Nye The Science Guy #119 : Buoyancy and FAST FORWARD to the "Try this section" on making your own submarine in a bottle. Fast forwarding will eliminate the parts of the tape that are not applicable to this lesson. STOP and EJECT the video at the end of the explanation on fish bladders. At this point, announce to the class that they will now construct their own submarine in a bottle. Use the idea from Bill Nye or use the following method to construct a low-cost submarine that the students may take home. Prior to class, obtain small plastic micropipette and cut all but one centimeter off the drawn tip. Insert a small hexagonal nut on the cut tip of each pipette. If it is not a secure fit, use a glue gun to secure the nut in place. The nut gives the pipette ballast when placed in the water.

Distribute one plastic bottle and one modified pipette to each student. Tell the students they may use food coloring to color the water in their bottles. Show the students how to fill their pipettes three-quarters full with tap water. (Place pipette upside down in a container of water and squeeze. Water will enter the pipette when the pressure is released.) Show them how to check if their submarine will operate correctly by placing it in a tub of water. The pipette should float in the water. If the pipette sinks, the students should squeeze out some water. If the pipettes rises too high in the water, they should add some water. Tell them to fill up their bottles to the rim, insert their submarines, and put the caps on. Carefully examine the pipette diver as pressure is applied to the bottle. Ask students what they think makes the submarine move up and down in the bottle. (As the bottle is compressed, water enters the diver and makes it less buoyant.) Instruct the students to clean up their work area.

Tell the students that since they know why a boat floats and how air can be adjusted in a submarine to raise or lower it, they should be able to determine whether boats can be made of any material. Accept all opinions from the students.

INSERT Dr. Dad's PH3#2: Buoyancy - Sink, Float or Boat. START the video at the beginning of the canoe race. MUTE the volume in order to focus the students' attention on the design of the boat after the girl says "We just took this canoe to state championships and we are in first place in all the races and design and everything." Tell the students to make careful observations on the canoe the girls are carrying. PAUSE the video when Dr. Dad and the two girls sit down. Ask if this is an ordinary canoe. Ask if they notice anything special about its shape, design or material. RESUME the video and correct the volume so students can hear the girls discussing the various aspects of their canoe. PAUSE the video after the girl says "Concrete can be molded into any shape and it can hold." REWIND the video and play this part back if students need to review.

PAUSE the video after Dr. Dad says "How do you get concrete to float?" Ask the students if anyone can answer that question. RESUME the video to hear the answer. STOP and EJECT the video after the girl says "That's Archimedes' Principle."
Post-Viewing Activities
Collect the guided listening sheet and take a grade on it. Remind them that in today's lesson they learned why a boat floats and how a submarine dives through the water. Tell them that now it is their task to design a boat that will hold at least three times its mass in cargo. Hand out the post-viewing activity sheet entitled Some Boats Won't Float. Tell them they may use either wax paper or clay to construct their boats. After designing and constructing the boats, all questions on the activity sheets must be answered. Assign each team a number and tell them to mark their boat with their number and place their finished boat on the supply dispersal sheet when they are finished.

Allow the students access to the following building materials: wax paper, clay, bowls and water. Have several balances available for students, along with loading objects such as marbles, pennies or paper clips. Allow the students 10-15 minutes to construct their boat. After all boats have been constructed, instruct each student team the task of testing the boats of two other teams to see if they have met the criterion of holding at least three times its mass in loading material. Observe each team as they construct and test boat models. Ask if any team feels they have a boat that can hold more than three times its mass in cargo. Challenge all teams to discover the maximum load capacity of their boat. Remind them to follow the instructions on their activity sheets to discover the maximum load capacity of their boats in relation to their mass.

The design of the boat that can hold the most cargo can be analyzed by the class. (This design displaces the maximum amount of fluid.) Instruct students to clean up their work areas. Collect activity sheets when the class is finished.
Action Plan
Take a field trip to a boat-building facility to see how boats are designed and made.

Ask a boat builder to visit class and to explain how designs are created and how boats are built.

Have a Navy spokesman visit class to discuss warships and submarines.
Art: Students can draw pictures of boats or create boats from paper.

Engineering: Students can create and design a boat from cardboard that must hold a person and move in water at least 500 feet.

Geography: Students can research how geographical features influence boat construction. Students can determine if salt water boats are designed differently from fresh water boats.

History: Students can research the Titanic disaster or the life of Archimedes.

Language Arts: Students can write a story about life on a submarine or boat.

Math: The volume of actual row boats, canoes and kayaks can be mathematically calculated.

Science: Students can observe boats in a nearby lake. They can analyze how design and use of boat are related. Students can make notes on what types of designs provide a maximum load capacity.
Click here to view the worksheet associated with this lesson.

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