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: 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.