LAB
VI. BUOYANCY
Problem:
What is the relationship between the volume of a boat and the
weight it can hold?
DO NOT
BEGIN YOUR EXPERIMENT UNTIL YOU HAVE READ THE BACKGROUND AND ANSWERED
ALL BACKGROUND QUESTIONS.
Background:
You often hear of a boat sinking because too many people have
gone on board. Today you will learn how scientists and engineers
can predict what the maximum number of people should be on a boat.
Before you begin this project you should review some basic concepts
in buoyancy, and density.
Rember from
class that Density = Mass/Volume. To find the density of an object
we must first find the objects mass and volume. For the rectangular
boats used in today's experiment you must use the formula Volume
= length x width x height. To find the mass of the boat use the
triple beam balance.
Since the
density of water is equal to 1 gm/cu.cm., any object that has
a density more than 1 gm./cu.cm. will sink in water. As long as
the density is less than 1 gm/cu.cm the object will float in water.
What keeps the object floating is called the buoyant force. This
is the upward force of a fluid that exists because the pressure
of a fluid varies with depth. If the upward force is more than
the downward force the object will float.
Background
Questions.
1) What is density?
2) How do we calculate the density of a solid rectangular object?
3) What is the density of a mass block (34 g.) that has the dimensions
3cm. 6cm. x 2cm.
4) Would you expect the block to float or sink? Explain your answer.
5) What is the force that keeps objects floating called? Why does
this force exist?
6) What must be done to overcome the buoyant force?
Hypothesis:
Discuss with your group (and justify) a hypothesis to the question
stated in the problem.
Procedure:
1) construct
5 boats using aluminum foil. Each boat should have a height of
1cm. The base of each boat should be a square with dimensions
shown below.
NOTE:
Try to construct the boats using the least amount of aluminum
foil and NO scotch tape. Refer to you class notes. Remember
a boat that is 3 x 3 x1 cm. requires a piece of aluminum foil
that is 5 x 5 sq. cm. Then fold up the sides (each 1 cm.) to give
the boat a height of 1 cm. Discuss this with your group.
1) 3x3x1 cm.
2) 4x4x1 cm.
3) 5x5x1 cm.
4) 6x6x1 cm.
5) 7x7x1 cm.
2) Start with
the smallest boat. Fill the 1000 ml. beaker 2/3 of the way up
with water. Float the boat. Start adding pennies, one at a time.
Make sure not to put all the pennies in one location of the boat.
3) Count how
many pennies it takes to sink the boat. Repeat this for each boat.
4) Copy the
following table into your notebook.

Boat I 
Boat II 
Boat III 
Boat IV 
Boat V 
number of pennies needed to sink boat 





Mass of boat alone (this is a very small
value) 





Mass of boat with pennies 





Volume of boat 





density of boat without pennies 





density of boat with pennies 





Results:
1) Include your table in the results section.
2).Collect the data and plot a graph of the number of washers
needed to sink the boat (yaxis) vs. volume of boat (xaxis)
3) Include in your results section anything you observe of interest.
Discussion:
Include the following questions in your discussion
1) What
were the variable in this experiment?
2) What factors were held constant?
3)What is the common factor in each case for sinking the boats.
4) What is buoyancy and how does it relate to your experiment.
5) Would the shape of the boats make a difference? Explain your
answer.
6) What significance is the slope of the graph you plotted?
7) Is the mass of the boat a significant factor in the boat sinking?
Explain your answer.
