Contributed by: Engineering K-Ph.D. Program, Pratt School of Engineering, Duke University

Lesson: What Floats Your Boat?

buoyancy ,  density ,  Archimedes' principle ,  displacement ,  water pressure

Keywords

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.

Learning Objectives 

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)

Introduction

Main ConceptBuoyant 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.

CLAY BOATS: Objectives

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 paperMasking Tape (white tape)

CLAY BOATS: Materials

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.

CLAY BOATS: INTRO

Part 1: 5-10 minutesTape 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.

CLAY BOATS: Create an object that will Float

Part 2: 15-20 minutesRedesign 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.

CLAY BOATS: Design a boat that can carry the heaviest load.

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.

Continued

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.

BUOYANT BOATS: Objectives

Electronic Balance600 mL plastic beakerBuoyant Boat Worksheet60 grams of clayAluminum tray to catch overflowing

waterPaper TowelBlue Grease Pencil

BUOYANT BOATS: Materials

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.

BUOYANT BOATS: Procedure

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?

Assessment:

Boat DesignHull form and function

Introduction

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)

T-Foil Motion Control System

Fully Submerged Hydrofoils

FOILCATS (Catamaran Hydrofoils)

SWA Monohull with Outriggers

Comparison

Air Cavity Monohulls and Catamarans

Wave Piercing Catamaran

Wing in Ground Effect Yachts (Ekranoplans)

Archimedes' Principle

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.

Assessment