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3C Issues in Technology #4
Other factors, such as cost, safety, appearance, environmental impact, and what will happen if the solution fails also must be considered....
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Buoyant Boats
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Purpose
To design and construct a boat that takes into account factors such as buoyancy, the properties of materials, and design constraints.
Context
In this lesson, students will design and construct
a boat out of aluminum foil and a few other simple materials. The boats
will then be tested by floating them in a pool or sink of water, and then
adding mass until they sink. While students may not be able to articulate
it, they will intuitively begin to understand the scientific laws required
for the design of the boat, i.e. buoyancy and Archimedes Principle. They
will also explore the shapes of boats and construction techniques that may
work for the boats.
"Research suggests that some high-school students believe that scientists
and engineers are more capable of making decisions about public issues
related to science and technology than the general public." (Benchmarks
for Science Literacy, p.
335.) Experience with designing solutions will help students to
feel more comfortable making decisions related to technology. This lesson
builds on the idea that "there is no perfect design. Designs that are
best in one respect may be inferior in other ways." (Benchmarks for
Science Literacy, p.
55.)
The introductory essay for the 3-5 Structure of
Matter benchmark states, "Objects and materials can be described by
more sophisticated properties—conduction of heat and electricity, buoyancy,
response to magnets, solubility, and transparency." The motivational
activity for this lesson addresses that statement. Although not the
major focus of the lesson, students should have a basic understanding
of the concept of buoyancy as a prerequisite for completing this lesson.
For that reason, this lesson should follow some instruction on buoyancy.
Additional activities may also be helpful to reinforce the concept after
completing these activities. (See the Extensions for some suggestions.)
Planning Ahead
- Several objects that float, and several that sink (e.g., blocks of wood, pieces of plastic, coins, washers)
- Beakers (or other containers) of water
- Materials to build a Cartesian Diver (empty soda bottle, dropper/pipette)
- Clay
- Aluminum foil
- Craft (popcicle) sticks
- Toothpicks
- Straws
- Tape
- Glue
- Small masses (e.g., coins, washers, nails, beans)
- Scales/balances
- Several sinks or containers for water
- Rulers
- Buoyant Boats student sheet
Motivation
Will it sink or float?
To do this introduction, gather several objects
that sink and several that float for each group of students. Recommended
materials include blocks of wood, pieces of plastic, coins, and washers.
Break the class into small groups and distribute
the objects and a beaker of water. Have each group predict which of
the objects will float and which will sink. Then have them place each
object in water to test their predictions. The students should then
describe the properties of the objects that sink and the properties
of the objects that float. Lead students to describe the buoyancy
of each object.
Next, show students a "Cartesian Diver." To build
one, you simply need an empty soda bottle (remove the label) and a dropper
or pipette. Fill the soda bottle to the top with water. Draw water into
the dropper until it is about half full and place it in the soda bottle.
The dropper should float. (If it sinks, you need to remove some of the
water from the dropper.) Put the cap on the bottle. When you squeeze
the bottle, the dropper should sink. (If it does not sink, you need
to add a little more water to the inside of the dropper.) The dropper
sinks when the bottle is squeezed because the pressure exerted on the
bottle is transferred through the water and compresses the bulb of the
dropper. This draws more water inside the dropper and increases its
mass (and therefore its density). When the pressure is released, the
water is forced out of the dropper and it floats again.
Have students try to
figure out why the Cartesion Diver floats and sinks. Be sure to lead
the explanation to the change in buoyant force on the dropper. The dropper
displaces a fixed amount of water; therefore, the buoyant force is fixed.
When water is added to the dropper, it weighs more than the buoyant
force and sinks. When water is removed, it weighs less then the buoyant
force and floats.
Development
Begin by explaining to the students that they will
compete in a boat-building competition. The goal is to build an aluminum
foil boat that will support the most weight. But, in order to build the
boats, they must use and understand the scientific law of buoyancy.
Buoyant force is the upward force that keeps things afloat. The buoyant
force is equal to the weight of the water the boat displaces. To review
buoyancy, have the students explore Buoyancy
Basics, on the NOVA Online website. Discuss the diagrams and make sure students understand
that the weight of water displaced equals the weight of the wood.
Once students understand the scientific principle of buoyancy,
they must consider some engineering principles that will be taken into
account when designing their boats. For upper-elementary students, these
will be simple principles like overall dimensions and shape. You could
have students experiment with a piece of clay, molding it to determine
shapes that will float the longest. Students should start to formulate
their own ideas of density, although specific terminology is too sophisticated
for this grade level. For example, students should realize that the
clay (and heavy things, in general) will sink unless shaped a certain
way (e.g., like a boat). They should also begin to understand that the
reason for this is the 'empty space' in the shape.
The final considerations are the properties of
the materials and the design techniques that might be used. Give each
team of boat builders a small piece of aluminum foil (a 10-inch square
will be enough), two toothpicks, a craft stick, a straw, some glue, and
some tape. Give students ample time to experiment with those materials
and have them answer these questions:
- What happens to the aluminum foil if it is repeatedly folded?
- Will the glue and/or tape stick to the foil?
- How can the toothpick and craft sticks be used to support the foil in the water?
Now, distribute the student page Buoyant Boats and the
materials listed on that page. Make sure the students understand that
they only get one piece of aluminum foil to build the boat. If it tears
or gets a hole, they must find a way to repair it. The rationale for
getting only one piece of foil is to reinforce the idea that there are
limitations to the materials they are using, and that not all attempts
will be successful given the constraints for those materials. It will
take the students one to two 45-minute periods to build the boats. Once
they are constructed, they are ready to be sunk.
For the competition, each boat should be floated
in a pool or sink. (If you do this in a pool, you will need some volunteers
to retrieve the sunken boats from the bottom. Be sure that your volunteers
move gently in the pool. Waves will wreak havoc on other boats.) Each
team should slowly and carefully add masses to their boats until they
sink. The last mass added, the one that finally puts the boat under,
should be removed, and the rest of the mass totaled. The boat that held
the most mass is the winner.
Assessment
Evaluation of the project should be based on the design
of the boat. How well did students' designs reflect what they learned
about the scientific law (buoyancy), engineering principles, properties
of materials, and construction techniques? The analysis questions on the
student page can also be used as part of the overall evaluation.
Extensions
You can extend the ideas in this lesson by using the Science NetLinks lesson, Engineering Solutions, which has students explore the side effects of technology, and design, implement, and evaluate solutions related to the problem of waste disposal.
The Saskatchewan Education page has several ideas that will help reinforce the concept of buoyancy.
Created :07/01/2002
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