Contributed by: Engineering K-Ph.D. Program, Pratt
School of Engineering, Duke University
 buoyancy , density , Archimedes'
principle , displacement , water
pressure
 Students will be able to state Archimedes'
principle of buoyancy.
 Students will be able to define a buoyant
object as one whose density is less than that
of water.
 Students will be able to describe how water
pressure acts in opposition to gravity in
order to make buoyant objects float.
 Lets look at some pictures to understand
why some things float and why other sink.
 Pay attention to
 Gravity (G)
 Buoyant force (B)
 Buoyant force pushes things out of water.
 Gravity causes things to sink.
 Which ever forces is greater wins.
 Buoyant force equals the weight of water
that is displaced.
 Students will be able to describe a means to
make a material that is denser than water
(modeling clay) float.
 Students will be able to describe the
parallels between the design process used to
create a dense but floatable object, and the
scientific method of inquiry.
 120 grams clay exactly (weigh using scale)
 One plastic container to fill ¾ with water
 Assorted weights (5gram, 10gram, 20 gram,
100 gram, …) Located in yellow plastic
organizer.
 Wax paper
 Masking Tape (white tape)
 Get into groups that you were in for the
density lab.
 Obtain all materials listed on the previous
slide.
 Will the modeling clay float or sink?
 Make a ball of clay and put it in the water.
 Part 1: 5-10 minutes
 Tape wax paper onto the table to create a
clean work station.
 Do not assume that a boat shape is ideal.
 Measure out 120 grams of clay and place
the lid tightly back on the container.
 Make sure you dry the clay with paper
towel after you test your boat.
 Part 2: 15-20 minutes
 Redesign you boat so that it carries the
largest load possible. Make sure your boat
does not get to wet. Water will cause the
clay to get soft.
 Use the weights in the yellow organizing
container as your load. Start out with a
small load and see how much it can carry.
 If you need more precise masses (smaller)
use the washers.
 If using washers you will need to weigh your
total mass using an electronic scale.
 When satisfied with your boat leave it to dry
overnight on the front table.
 Students will be able to describe a means to
make a material that is denser than water
(modeling clay) float.
 Students will be able to describe the
parallels between the design process used to
create a dense but floatable object, and the
scientific method of inquiry.
 Electronic Balance
 600 mL plastic beaker
 Buoyant Boat Worksheet
 60 grams of clay
 Aluminum tray to catch overflowing water
 Paper Towel
 Blue Grease Pencil
 Follow the instructions on the Buoyant
Boats handout.
 Answer all questions and record all results
in a table on the back of the paper.
 You will need to make your own table.
 What was the question being asked in this
experiment?
 How did the mass of the displaced water
compare to the mass of the lump of clay?
 When you repeated the experiment with
other amounts of clay did you get similar
results?
 Boat Design
 Hull form and function
 Flat bottom boat will likely be the best for a
clay boat.
 Flat hulls are faster but rougher ride. (bass
boat). Also allow you to go in shallower
waters.
 Deep v hulls are slower but cut through the
waves giving a smoother ride. (salt water
boats and cruisers)
 Write a paragraph that explains why the
three objects do not float in water in quite
the same ways.
 Write a paragraph that explains why a lump
of clay will sink in water, but the same
volume of clay, when shaped like a bowl, will
float in water.